Right, but then at the end of the day, when Andy's handing out his toys to the little girl, he could have said, "Oh, whoops, how did this get in here? Nope, sorry, you can't have him."
I think it was perfect. It was better that way. The toys got played with one more time by Andy AND their new owner. It was like the Star Trek movie that had the original enterprise crew working with the Next Generation crew, to transition the viewer into being okay with the Next Generation crew. They're pals, and you're okay with it.
Plus, Andy was going on to college, and Woody didn't need to see his friend fall apart to sex, drugs, drunken vomit-covered-pass-out sessions and whatnot.
Plus, there was a guitar in Andy's room, so you know he's gonna start a band, get drunk and then complain on a messageboard about how nobody ever comes to see his band play. And that shit's just sad.
The toys are in a better place right now while Andy experiences his 'lost' years.