You must have been lucky in the Hampton Inn properties you've stayed at. There is in fact WIDE variation among them. Some are very basic, no-frills places with obviously cheap furnishings, small windows, and limited breakfast options. Others are much, much more luxurious. Some have microwaves and fridges in the rooms, but most do not (at least in my experience). Also, there is typically NO restaurant. (There have been other threads on Hampton Inns, including a long one devoted to reviews of HIs in various locations.)

I find HGI to be VERY different from HI. Most HGIs seem to be pretty new and much more uniform than HI. There is always a fridge and microwave in the room at HGI; always a pantry, a business center with free internet access, and (I believe) free high-speed internet in the rooms. There is a restaurant onsite, and it doesn't just serve breakfast, but other meals as well. In sum, you get a lot more than the no-frills experience, and rates are set accordingly.