Both KDE and GNOME follow the same basic cycle: large dramatic changes in infrastructure and layout are followed by years of relatively small, incrememental changes. How many years did KDE go between 2.0 and 4.0? (KDE 3.0 was a break in ABI but the infrastructure and layout were largely the same.) And how many years have there between GNOME 2.0 and the planned GNOME 3.0 next year?
The big difference right now is that KDE made their big change last year and are now incrementally fixing, improving things. GNOME, on the other hand, are working on their big change, which will land next year. The cycle is the same, but the two projects are on different parts of this cycle right now.
There are a couple smaller differences, as well. First, as I understand it, KDE developed many parts of their new infrastructure for a couple years, and this infrastructure landed for use at KDE 4.0. GNOME seems to be inserting many pieces of its new infrastructure in the GNOME 2.x cycle before putting all the new pieces together in GNOME 3.0. On the one hand, this means that the various pieces will (hopefully) get more testing, and thus more bugfixing, before 3.0. On the other hand, 3.0 becomes a little bit less exciting because piece x and piece y are not exactly new. The second difference is that Qt underwent a big overhaul for its 4.x series, which forms the basis of KDE 4.0, whereas GTK 3.0 will be cleaned up, rather than radically changed.
This does not mean that big new technologies are not going to be in GNOME 3.0. Clutter, gjs, seed, and gnome introspection, to take a few examples, are separate libraries that will form the backbone of GNOME 3.0. It seems to me that tech journalists hear the news about GTK+ 3.0 and decide that GNOME 3.0 will have no changes. That should not be the case at all: next generation GNOME shell