That's exactly it. They've always been one step behind for hardware generation.
When WP7 came out it only supported Snapdragon S1. This was during the time all the other competitors was using Snapdragon S2.
When WP7.5 update came out, Snapdragon S2 was supported. By this time everyone jumped onto S3 and S4.
When WP8 came out, Snapdragon S4 dual cores were supported. For about 6 months or so they were on par hardware wise but then the competition jumped to the Quad cores (namely snapdragon 600), and WP8 devices were stuck with the dual core S4s. Low end was fine cuz everyone used the same low end, but high end was a problem since WP could not compete.
WP8 GDR3 update added support for quadcore Snapdragon 200, 400 and 800 (I dunno about 600...I think they're skipping that one which is fine). There doesn't appear to be 801 support and there may not be which in all honestly doesn't matter much because its just a speed bumped snapdragon 800 (like 10-15% at most if its noticeable at all).
Heck the HTC One M8 uses a snapdragon 801 but its CPU is still clocked the same as the 800 (2.26ghz), so CPU wise nothing changes. The changes only comes from a higher clocked GPU (which again is the exact same Adreno 330, but clocked at like 583mhz vs 450 or something) and I think a faster memory interface. Technically WP should be able to use the 801 since the 800 and 801 are the same (one is just a bit faster).
Not sure if 805 support is coming in the initial WP8.1 release but word is it will be in WP8.1 GDR2 which is set for later this year apparently. And so far, there is nothing that uses the 805 chipset since its not ready yet.
The 805 is the beast that everyone should be whining about IF it was being released on the androids right now while the WP devices are still using the 800. but that isn't the case.
Snapdragon 805 has a newer CPU: The Snapdragon 800/801 uses KRAIT 400 CPU cores, 805 uses KRAIT 450. GPU is newer too, 800/801 uses Adreno330, 805 uses Adreno 420. They claim something like 50% improvement over the 800/801 and every year they've been saying 'console quality graphics'