The windows phones where behind Android and iOs phones in screen resolution and CPU cores somewhat before this upgade. Not baddly but a little bit. Two cores where maximum and screen resolution was 720p or something like that. Not bad specks and still the most sensible to have from battlery usage perspective!
So not anything too important in that respect! The next big upgrade in Windows phone hardware would be maybe even higher resolution (for phablets) and 64bit prosessors, but there is no hurry in there. Maybe at the same time they plan to put WinRT and WinMP together in 2015...
Core count alone is completely irrelevant. WP7 was designed to be as efficient as possible on a single core and it ran as smooth and crisp as any Android on a dual- or quad-core chip. I believe dual-core support on WP8 is more about marketing than performance since consumers think they need more cores even if the OS doesn't. The fact that WP is as responsive on lesser hardware as Android is on blazing fast chips is a testament to WP's efficiency and Android's poor optimization.
Higher resolution screens also means higher power drain. The 1280x768 4.5" screens are higher PPI than Apple's first "Retina" displays and you have to have your face less than a foot from the screen before you can identify individual pixels. Again, nothing to brag about, but nothing that's holding it back either. Just another marketing blurb that doesn't actually impact use of the device.
I think it's less that WP couldn't support higher-end hardware rather than a conscientious decision that such hardware wasn't necessary.