Desktops are taking a hit from desktops!
There are still acres of desktop real estate which is going to be replaced with more desktops.
Looking at this at a high level, there is actually pretty much sod all difference for the average user in the last 5-6 years technology-wise on a "desktop PC". They are just not buying them because nothing is compelling them to upgrade as they are fine as they are.
If there was a technological leap then we might see something but for most users, a 5-6 year old desktop would run the latest and greatest version of Windows fine.
Tablets are going to be a short lived "experiment" which will dry up in time, much as they always have been (Apple are far from being the first tablet vendor). Microsoft may have the answer to that in a hybrid device but we'll see.