Actually Six says some very nice things about Jamie in The Two Doctors. "I was always rather fond of Jamie" for example, and given his Doctor wasn't especially warm towards anyone it would have been weird if he had got all teary eyed!
That's right, I forgot about that line, which is indeed rather high praise coming from Doc #6.
I guess I always focused more on how indifferent Doc #6 was when Doc# 2 and Jamie left.
Also, back to my earlier feeling that earlier writers and producers didn't feel they were the same person, when Doc #2 takes out the TARDIS remote control and Doc #6 cries something along the lines of, "Where did you get that? I've always wanted one!" Uh, he should know where he got it, and unless he's lost it (which I suppose is very likely, given the Doctor) he should still have it. Doc #2 says that privledges such as that come with age, except that Doc #2 is the younger of the two. The actor is older, but the character is younger. Tough concept to get your ahead around, I suppose.
In the five Doctors they kept calling Doc #5 "the kid" or "the young one" or things to that effect, and they treated Doc #1 as the wise old man, instead of the arrogant youth he likely would have been seen as (imagine you are 72, and and meet yourself at ages 54, age 36 and age 18. You'd probably find your 18 year old self an insufferable youngster, and your 18 year old self would probably think he's more clever than the lot of you combined.)
Given how young the actor who played Doc# 5 was, it would have been really funny if the other Doctors all called him an old geezer, and treated his young body as signs that he's having a sad little midlife crisis.