In short: It's just a freaking domain :)
blog.ch played certainly an important part in bringing the swiss bloggers together, but nowadays it's neither unique nor very innovative. slug.ch, list.blogug.ch and planet.blogug.ch are already replacing the aggregator features of blog.ch with more features, more blogs and also a more open approach.
Sure, Matthias' posts about blogging are most of the time interesting and I do hope, he continuous in doing so. But with the introduction of the blogch tag (search on the Planet), a more decentralized and distributed discussion about the swiss blogosphere will hopefully emerge.
So, if Matthias wants to sell blog.ch to some commercial entity, so be it. It's his domain, he invested a lot of time in it and he can do with it, whatever he wants. Whatever happens with blog.ch, alternatives are already here and I'm sure, the community will do the needed promotion, if necessary. And it's not that one automatically types in “blog.ch”, just because he wants to know something about blogs in switzerland (and never heard of blog.ch before). The rest is solvable by linking, mouth-to-mouth (or blog-to-blog :) ) propaganda and the inevitable PageRank. If blog.ch becomes “bad” (and that doesn't necessarily have to happen, even if it will be “commercial”), it's really just a tiny short-term problem for the community.
Lots of people suggested also, that blogug.ch should take over blog.ch. Sure, not a bad idea, which I'm definitively not against, but as I said, it's just a domain …
And all the talk about “Doing a blog Verein” etc… FCS, why do we always need a “Verein” for each and everything. blogug.ch for example as it is now, works pretty well, I do the planet, ping and top100, Patrice does the stats and list and Alain owns the domain, provides the DNS services and the gallery. Each on his own server. And everyone is welcome to contribute, come up with new ideas and gets his own subdomain. I don't see, how a “Verein” would help here, besides having to invest a lot of time into the “legal stuff”. But maybe I'm just too used to work on loosely coupled communities, which do work together as it fits and it works fine most of the time (The PHP community for example still has no “Foundation” or whatsoever).
To sum up: blog.ch has a hard time keeping up with the newly emerging alternatives and without any major overhaul (or cooperation) would be getting more and more obsolete anyway. So it's the right time for Matthias to sell it now, before his zenith is way behind him :) I wish Matthias much luck, hope he will find more time for his family in the future and thanks for all the work he did for the Swiss blog community (and sincerely hope, he won't disappear completely)
Update: kblog has a long post about, why blog.ch should be a “Verein”. I understand his reasoning, but still don't agree :)