Canon and Nikon were dominating the camera market even before IBIS or digital cameras were invented. Many professionals and enthusiasts already owned a collection of excellent Canon or Nikkor lenses when the digital revolution came. Thus when the big two introduced their DSLRs with backward lens compatibility (with EF and F mounts respectively), it was natural for their users to continue with their existing systems which they had heavily invested in.
On the other hand, Olympus and Panasonic are on almost equal footing in the micro-4/3 market. The 4/3 system is relatively new and the micro-4/3 is even newer. Both of them are not backward compatible with any legacy system (adapters aside). Although Olympus entered the 4/3 market first and developed some awesome Zuiko Digital lenses, they are quite large and do not attract users who buy into m4/3 for its small form factor. So the advantage Olympus has over Panasonic is very small.
In such a competitive market, where the target audience is expanding from photographers to the less-enthusiastic consumers, any technological advantage such as IBIS will be a big selling point. Whether it is the best solution is beside the point. But as a photographer, I think it is a good solution. Camera bodies come and go, but good glass lasts a long time. By having the IS mechanism, which is essentially a moving part that can wear out, in the more-often-replaced body, we are actually simplifying maintenance and possibly reducing the long term cost of ownership. This is especially true if you intend to (or already) own a large collection of lenses, particularly non-IS lenses.
Just think about how much more the Voigtlander 25mm f/0.95 costs over the Leica 25mm f/1.4. It's almost $500 for that one stop, plus all the sacrifices in optical quality, size and weight to achieve that ultra-large aperture. For low-light action shooting these sacrifices are necessary since no IS can help stop action. But for everyone else, IBIS can serve a similar purpose for less money. And it works for all lenses.
In case you are wondering, no, Olympus did not pay me to extol on the IBIS. This is my personal take on the technology, which contributed to my decision to buy the E-M5 over the GX-1, and to replace my existing 60D.