I reckon there are some factors that if you wanna say 'G1' you cant really mess with such as:
*Optimus turning into a Truck and being a very noble character
*The Dinobots being loose cannons and Grimlock challenging authority
*The Constructicons turning into Devestator
*Soundwave & his cassettes
*Intergalactic adventures
*A contingent of Autobots and Decepticons on Earth with earth-based vehicle modes
*Megatron with his lieutenants being Soundwave, Shockwave & Starscream
*Cyberton and Unicron
*Starscream being self-serving
*Wheelie being annoying
*Civil War
*Transformation
I reckon Dreamwave did the least mucking about with the G1 canon and stayed pretty true to the cartoon roots.
Funpub just did what they liked really.
I think middle years of IDW were pretty good in staying true to the G1 canon. The first year they were finding their feet so could be excused for doing some odd stuff. The last 12 months has been sadly disappointing with plot lines that don't go anywhere, romances that make no sense forced upon some character whilst other characters just act contrary to their established personas (there is a difference between a character growing and a character being changed just for the hell of it), and too much conflicting info. Think they ran out of good ideas a while back to be honest - even Lost Light is beginning to lose its appeal and I count them among my favorite TF comics ever.
Do you reckon Marvel and Marvel UK are caconical? Hard to tell for me.