They don't get as much flack within the industry with this practice because they usually tend to go for the best-suited voice rather than simply the biggest names on the market. For instance, Finding Nemo's leads were voiced by Albert Brooks and Ellen DeGeneres while DreamWorks's Shark Tale was headlined by Will Smith, Angelina Jolie, and Robert DeNiro, whose names dominated the film's marketing and whose characters were very much ink suits.
Hey, It's That Voice!: Pixar employees sometimes voice their characters rather than hiring outside actors. This results in some recognizable voices between the different films.
John Ratzenberger has done a voice in EVERY Pixar movie to date.
Brenda Chapman's version of Brave. We may never be sure why she was laid off, but it seems to have disappointed a lot of people in the industry, including some Pixar employees.
In fact, anytime Pixar replaces a director on their films (which so far only happened a few times, thank goodness) will get this reaction. Brad Bird was put on Ratatouille at the last minute and had to work with revising the script and making the rats less anthropomorphic than what the original director had. Of note, Chef Gusteau was to be alive through the whole movie instead of an imaginary being.
On the otherhand, when Pixar and Disney first merged, part of the deal was John Lassester becoming the new head honcho of the Animation Department. His first order of business was completely overhauling Meet the Robinsons and Bolt. Considering the massive changes made, it'd leads one to wonder what the original product of both films would have been like.
Toy Story was almost the victim of Executive Meddling thanks to Jeffrey Katzenberg. Katzenberg continually pushed for a more adult, cynicalToy Story, making Woody even more of a jerkass and relying heavily on insult humor. The result backfired horribly; at a screening for the Disney execs, Roy Disney declared it the worst thing he'd ever seen, and Disney was ready to scrap the whole project until the writers were finally left alone to write the story they wanted to write. The rest is history.
The sequel, mandated upon by Disney, was planned to be released Direct-to-Video. However, Pixar put so much effort into it that it convinced Disney to release it theatrically.
Later on, Pixar also had to deal with Michael Eisner. During the Disney v. Pixar negotiations, Eisner created Circle 7 Animation, which would have made Disney-brand sequels to Pixar films including Toy Story 3 which would have seen Buzz Lightyear recalled to Taiwan. However, he was fired, the studio got shut down, and Disney purchased Pixar. Eventually, Pixar would create the TS 3 we all know and love.