I'm not a big fan of the FO3/NV style, where having enough Speech gives you the best ending on a silver platter while apologizing for ever being in your way
I remember in Dead Money (you know, the one about letting go even though several players tried to ignore the lesson as hard as possible by carrying out an item that most vendors wouldn't even have the caps to fully pay you for?), there was one character where a speech check would actually be a dialogue trap of sorts in that, when you were separated and reunited with them later, they'd try to kill you rather than, if you were the one being subservient to them, being willing to help you. This dialogue trap would occur whether you had the skill points to succeed or not, if memory serves.
While that does make speech a more interesting option than the NV/FO3 style (and certainly not some luck-based "pretty please" like FO4), that does come with the problem of potentially pissing players off by making them pour skill points into something that either doesn't work or actively works against them. Making speech a challenge of choosing the right dialogue would mean that, short of SPECIAL stats preventing you from saying certain things (the way low intellect in 1 and 2 would cause your character's speech pattern to be dramatically different than normal speech), any character could smooth-talk their way out of a scenario that could be smooth-talked out of, with enough save-scumming. Combining the two would likely take additional time in either programming, writing, or both - and if memory serves, Fallout New Vegas's development was somewhat rushed.