Tulsidas and Vyasa could not endure the idea of Ravana touching the thighs of Sita, even for the purpose of abducting her. Hence they have 'excised' the reference to the thighs and rewritten the sentences in a euphemistic style:--
Context: Ravana abducting Sita in the forest
VALMIKI RAMAYANA - BOOK OF FORESTS - CHAPTER 49 - VERSE 17
vaamena siitaam padmaakshiim muurdhajeshu karen`a saha
uurvoh tu dakshin`eena eva parijagraaha paan`inaa. 3-49-17
Gist: Ravana lifted Sita with his left hand holding her hair behind her neck and with his right hand holding her thighs.
Mahabharata Aranya Parva Chapter 262 Verses 39-40
ta`m anudrutya sus`ron`i`m ra`van`ah pratyashedhayat
bhartsayitva` tu ru`kshen`a svaren`a gatacetana`m
mu`rdhajeshu nijagra`ha kham upa`cakrame tatah
gist: Ravana seized Sita by her hair-and-head and flue into the sky.
Ramcharitamanas of Tulsidas, Aranya Kanda, verse 28.
krodhavata taba raavana liinhisi ratha bait`haayii,
calaa gaganapatha aatura bhayaam ratha haan ki na jaayi.
Gist: Ravana was full of anger. Ravana leaped and made Sita to sit on the chariot. He flew to the air in a state of trepidition. He was unable to drive the chariot.
Valmiki could not avoid describing the thighs of Sita. Vyasa in his Mahabharata (through the mouth of Markandeya. Markandeya told Yudhisht`hira, the story of Rama) avoided the thighs, but retained Ravana holding the Sita's hair.
Tulsidas was first a devotee and then a poet. He left away both the hair and the thighs of Sita. Tulsidas straight-away made Ravana to place Sita in the chariot.
Valmiki spent about 16 verses for the conversation of Sita and Ravana. Tulsidas completed the whole interview in just four verses, using a narrative style.
All the three poets are silent here about the magic line drawn by Lakshmana called 'Lakshmana Rekha', which Ravana could not cross owing to raging fire. Ravana freely-unhindered enters the cottage and abducts Sita. I found at one internet site, that Tulsidas referred to Lakshmana Rekha in lankA kAnDa, in the context of manDOdari counselling rAvAna, on the perils of war with Rama. I tried my best, I could not trace it anywhere in rAmcharitamAnas. Knowledgeable readers may please help me.
I understand that Telugu poetess Molla used the Lakshman Rekha concept in her Molla rAmAyaNaM of the 16c. fame. I, however, feel that we need not take vernacular rAmAyaNAs -- translations or otherwise, including Hindi rAmAyaNA rAmcaritmAnas with extreme seriousness for analysis. Their greatness rests with their 'devotion or bhakti bhAvA' or 'sincerity or ShraddhA bhAva' and not adherence to exact literal translation of vAlmiki rAmAyana.
Mahabhagavata too contained the story of rAmA (rAmAyaNa). Book 9 (navama skandham), Chapter 10, verse 11.
raakṣhsAdhamEna vṛukavad vipinee asamakṣam
bhrAtrA vanE kṛupaNavat priyayA viyuktaḥ
strI-samginAḿ gatim iti prathayams cacAra
Gist: The worst of the demons Ravana abducted Sita (who was unprotected in the absence of Rama) like a tiger seizing an unguarded sheep. Rama, separated by his wife, wandered in the forest with his brother, like an accursed person.
Sage Suka (Parrot) was the narrator in Mahabhagavata. The accursed King Parikshit was the listener. Suka renounced this world from his birth. The object of Mahabhagavata is to promote devotion to VishNu and renunciation. Suka used the opportunity to comment on Rama himself. He quoted Rama as an example of the class of persons who get attached to women and end up as miserable sufferers.
Suka told Parikshit that he was narrating Rama's story briefly because the king might have heard about rAmA many times in the past. In the midst of this brevity, Ravana's kidnapping Sita was disposed off just in one verse. Nothing about the manner in which Ravana abducted Sita could find a place in Bhagavata narration, not to speak of Sita's hair, neck or thighs.
This does not mean that Bhagavata was brief everywhere. Bhagavata's focus was more on Krishna's childhood and his deeds, so much so that one entire book 10 (dasama skamtham - the largest among the twelve parts of Maha Bhagavatam) was devoted for the purpose. Bhagavata's avowed purpose was to describe the ten incarnations of Lord Vishnu among which Rama's was the seventh and Krishna's was the eighth. Krishna's story received maximum attention whereas Rama's story was dealt with like a Cinderella .
My guesswork: One probable reason for this Cinderella treatment meted out to Rama's story in Bhagavata may be : The rulers who patronised Mahabharata and Mahabhagavata were apparently from YAdava, bhOja, paramAra clans of Malva, Vidarbha (modern Nagpur, Indore, South Rajasthan, East Gujarat area). The kings who patronised Rama were apparently more from Eastern MP and Eastern UP. The balladeers of yore had a gratitude(inous) compulsion to eulogise the clans of the sponsoring kings just as the newspapers and tv channels of today gratefully publish/broadcast paid news of business-houses and political parties.
The reference to Ramayana in MahAbhArata was also brief in relation to its monumental size. The narrators of Mahabharata-- VaisampayAna, mArkanDEya etc. were not as staunch VaiShNavaiTs as SukA was. Besides, the listener of MahAbhAgavata Parikshit was grateful to Krishna for saving his life in mother's womb when attacked by ASvaththAma. Probably, Parikshit might have nursed another hope within himself that Krishna would save him again. The listener of mahAbhArata janamEjaya didn't have such direct attachment to Krishna as his own father ParIkshit had. JanamEjaya was consuming himself with an urge for revenge against the serpant Takshaka who killed J's father ParIkshit.