"Could it not be that people are waiting on Windows 10's release"
Unlikely since Windows 10 is coming to the computers regardless if people buy the computers now or whenever Win10 is released. The "Joe Sixpacks" out there are not even aware of the Windows 10.
Few small shops may wait for it just to standardize into something else than Windows 7 (all support ends in less than 5 years from now), or Windows 8.1 (many people dislike it).
AFAIK, Win10 will be free upgrade also to businesses that are using OEM versions of Windows Pro for the first year so the computers can be bought now if necessary and upgraded later though it may be inconvenient for some.
ERPs, VPNs, drivers and other software may need updates to work with Win10 and usually it takes at least months (or even years) to get certification for the latest Windows version.
"Also factor in that as each successive release of Windows seems to require less horsepower and a generally depressed economy is it any wonder PC sales are down when money's tight you mend and make do!"
I agree. Also, a 5-year-old Intel i5 isn't noticeably slower in general usage than the latest i5 CPU's - AES-NI does make a noticeable difference but to how many people? Just replace the HDD with an SSD and that's it. For many people even a 64GB or 128GB drive is more than enough and the cost of upgrade is minimal.