Apple prohibiting iPhone apps which compete with own interests

It'll be interesting to see how the restrictions on installing iPhone apps (such as Apple being able to restrict the types of apps available) play out in this market.

Mac OS X, obviously, has been a system where you can install anything, including competitors' applications (like Adobe Lightroom, Adobe Premiere, etc.) Windows Mobile has been a mostly free-install platform as well. Is the mobile market with the iPhone any different?