A lot of startup business models involve building products that fill gaps in existing platforms. There is absolutely nothing wrong with that, and there have been a few success stories. But if you don’t own the platform, or if you aren’t wildly successful at filling the gap you’re taking a really big risk.
via The Dangers of Building on Someone Else’s Platform | trevoro.ca | blog. There is a definite and real danger to merely filling the gaps in other platforms, generally whatever you can do the company building the platform can do or buy the ability to do.