Wow, Beezer, you just had a head-on with the flat earth folk. Of course there's a difference in the sound between receivers, and more differences than are measured by a frequency response curve. I've owned enough receivers over the years to be able to say with confidence that there are major differences in sound quality from one receiver to another.
Among my personal favorites among low price units is the Panasonic SA-HE200 which I compared to the Harman Kardon AVR65, Onkyo 797, Sony STRDB1070, Sherwood something or other. The Panny did very well, sounded better than the HK unit.
Careful if you're considering bringing up the subject of speaker wire or interconnects. Some folks around here think string does as good a job and can get pretty riled up if you think there's anything better than zip cord.
Enjoy the Music. Trust your ears. Laugh at Folks Who Claim to Know it All.