There only is one sure strategy for avoiding the potential steamroller of the platform company. Don't build on the platform.
The risk is not very hard to assess. It's pretty binary per startup opportunity. Do the relevant incumbents' revenue models, distribution models, or inherent cultural limitations prevent them from competing with you. @paulsutter covered the first two well early in this discussion. For the last, Apple has great difficulty with social, Facebook hasn't figured out Touch, Google is excessively focused on those two competitors, etc.
Please also see these two comments: http://news.ycombinator.com/item?id=4336783 http://rafer.net/post/28638883246/mark-i-know-for-a-fact-tha...,