A movie ticket is a lot cheaper than a free flight, and a movie critic isn't selling a "You can have this life too." When movie critics have accepted trips etc, they have come under significant criticism. See, e.g., the HFPA award of a golden globe to Pia Zadora.
On the other hand, would you trust a Judge who's dinner tab was paid for by one of the parties appearing before it?
A big issue is that the movie critic is seeing the same movie as anyone else would, even if he(or his employer) didn't pay $10. When QR or SPG books a special trip for a blogger, it is not the same experience Joe Q. Public would have.
You're of course free to think that TPG and other bloggers provide honest reviews of the companies that fly them around the world for free. But at the least, disclosure is important so a reader can consider the source if they mistakenly went to his blog seeking honest advice.