Also, Debian staked out its ground as a open, community-developed, non-profit, non-beholden distribution long ago. Later community-developed projects have had to answer the question, "why shouldn't I just go with Debian?" There are lots of possible answers to that question (hence projects like Fedora, Gentoo, Arch, Mint, DSL, etc.), but it's still a question that has to be answered.
It's possible that in the not-too-distant future, the success of other community-oriented distros will start to raise questions for Debian, but so far, the momentum of being first/longest-lived and of being the basis for many other distros seems to be carrying them along quite well.
On the other hand, it seems to me that Fedora has established itself pretty well as the "help us guide the direction of the next release of the commercial system you're probably going to end up using at work no matter what you'd personally prefer" system. That seems to be working quite well for them. I'm not entirely sure why it isn't working as well for OpenSUSE, but it may have something to do with the respective degrees of community involvement of the associated commercial systems (Red Hat and Novell).