Momentum is strong in any major corporation. Google still has Exchange running for their people who refuse to use GMail (and for BlackBerry users). It's not just presentations...even at Google, a lot of people are afraid of new technology and continue to use whatever it is that they're accustomed to. And that makes sense, in many cases...if it takes a day to understand a new product well enough to use it to the same level you used the old product, you've just lost a day of productivity. Everybody does the math on the additional value that product provides them differently. Maybe for some, data portability is not a big enough benefit to overcome the lack of flashy slideshows, existing PPT templates they may have been refining for years, and the time it takes to figure things out.