That's exactly the reason why I have favoured GTK-based environments over KDE, even though I acknowledge that the API provided by Qt is probably the best I've happened to work with. GTK is owned by the community, and I know that as long as there's a passionate developer out there working on it the project is alive. When it comes to a product owned by Trolltech/Nokia/Qt Company...well, I can't be that sure.
The history of computing is already full of examples of open source projects that either died or have undergone complex forks and transition periods because the company behind them decided to pull the plug, or go for a different business model, or they went from being community-owned to being business-owned. As open source software is more and more commoditised, and unlike its counterparts it's expected to just build and run anywhere, without all the business fluff and hysteria around, we can't afford to let that happen.
However, purely community-owned open source software succumbs to the tragedy of commons on the long run - but that's a comment for another post.