Like in Nature it is about competition - if a pro looses ground because his competition makes better pictures/videos with updated gear - he just needs investing again (provided funding available). Buy always the latest modell and sell the used one to us hobbyists. If a pro is established and doesn't suffer loss of ground, pro can wait, companies too. If a pro waits and looses ground - he is not a pro anymore.
All the rest of the trigger-clicker community is like readers on a writers festival.
You'd have to have really appalling gear for that to make a difference, even the old 1Ds is still being used as a pro body today, and just to reiterate it's not the gear which makes a photographer good, it's the other way around!
I would never buy the latest kit, the problem is that it takes an age for Adobe & other software providers to issue their RAW / ACR updates, meaning that you have a camera which for professional use is just about useless. Oh I hear the cry you can convert to DNG! yeah well try converting 1000 files manually because DPP is the only software which is useable (yes I know it will batch them, but it's another unecessary step) then working through them all as DNG through the workflow software. If you're lucky the only glitch will be the software / firmware (A la 5D MkII) but it could involve a workshop visit (A la Nikon D5000 twice!).
A wait for 6 - 12 months on any new camera body is good advice - and the price usually drops to a more sensible level too.