I've definitely noticed this.

Another issue is that sometimes travel providers give rebates to companies depending on the amount of travel the company books. One client I worked for told me never to use another rental car company other than their preferred provider because of this. They said I might think I was saving the company a few bucks but actually I would end up costing them money.

I don't know if the hotel chains offer rebates or not, but I can almost always beat the corporate rate with a little shopping.