In 1, his eyes have lids molded on in toy mode; and I think the same thing for 2, but in 3, they’re wide open. These photos show Woody and Buzz in Sid’s backpack, Buzz Lightyear commercial, Buzz with Andy in 2, and Buzz in Sunnyside in 3
-Omar
My guess is that it’s a style change. They change a lot of things like that, and I’m beginning to think that it’s not intentional, like in the first Toy Story where the toys’ inanimate face would slightly reflect the situation, but carelessness.
I can see eye-lids on the eyes of Buzz in the picture of him in TS3…but maybe thats just me.
I noticed that too. I’m going to go with Dinoco, and just assume they just didn’t bother fiddling with the accuracy. 
I think Dinoco’s right because in the TS3 Commentary it talks about style changes.
Buzz looking more happy than serious in 3 made it more appropriate to be a girls toy…maybe they did it for that
I don’t think they should have changed his smile. That’s ridiculous. 
Yeah, his face was actually pretty prominant in the first two films, and something about his face always seemed a bit off before I pinpointed that they made him happier.
Bonnie or no Bonnie, I see no excuse for altering such a beloved character.
I think they were making him look more appealing as a toy upgrading his dead eye look from 1.
The whole reason for his serious look was that he was supposed to be a fearless superhero. But the grinning look pretty much reflects the toy Buzz’s personality. At least they didn’t make Woody open his mouth…
Oh my Gravy, if they had opened Woody’s mouth… 
…I would throw down. I still believe they should have kept Buzz’s signature power smirk, though. I don’t believe in altering characters that are known worldwide as being one certain way, sorry.
Where abouts in the movie was the scene of the second pic??? (I know I will go ‘oh yeah’ the second I hear when it was)
Buzz Lightyear commercial (probably from Kyle’s unfiltered YouTube video).
Ohhhhhhhhhhhhhhhhhhh
I actually prefer Buzz’s new smile to his “power smirk”, though they both work well for the character’s nature at the time. In the original, Buzz was more arrogant at first, whereas by the time of TS3, he has become more humble. Also, having that smirk works better for the “Strange Things” scene, whereas a more heartwarming smile works better for TS3’s many heartwarming moments, e.g. when he’s given to Bonnie.
Of course, I think we’re slightly nitpicking here, as I honestly didn’t consciously notice the difference until this topic. I would have noticed an open-mouthed Woody, though (or a closed-mouth Buzz, for that matter).
When it comes to the eyelids, it’s utterly ludicrous to expect them to keep them exactly the same purely for the sake of it, though I must admit I don’t see any reason to change them, save perhaps to make his eyes look slightly wider and thus cuter (for the previously mentioned heartwarming factor).
I think the smile is more appealing, but it disturbs me that they changed it. I have no logic, just an obsessive compulsive TS obsession.
I’m guessing it was deliberate by what we’re presented with in Toy Story 2. In the opening scene, Buzz is smiling a little more, and his eyebrows are in a softer expression. But all of the new Buzzes have the classic expression.
Now, I think Woody has a slightly different smile, but that’s really splitting hairs; Pixar probably had an intention, and I wouldn’tve noticed.