If we compare ourselves to the standards of a typical (and technical) SE site, we're pretty far from graduating beta because we don't have nearly the kind of stats they generally look for. However, that doesn't mean there isn't a place for Philosophy.SE; I just think that given the topic (philosophy being something relatively slowly changing, compared to our ever evolving understanding physics or biology or computer sciences) and the SE-imposed format (academic, focused questions, try not to "do" philosophy as much, etc.) that we are going to inherently have less content to work with.
However, there will always be those questions that are too "meta" for other sites which fit perfectly for us, and that I think is an important niche to have, among our primary purpose which is to be a place where people can ask specific, answerable questions about philosophy.
The admins probably do recognize the importance of this niche we fill on some level, but I suspect there is also politics involved. I.E., if they let a site like philosophy graduate beta with relatively low stats, they would have to deal with swarms of people complaining about their proposals being closed while having similar stats. That's probably something they don't want to deal with, and so we stay beta.
Ironically, graduating beta may actually give us the boost we need, since I think a good number of people leave because they don't think the site will last and don't want to invest their time and effort only to have all their points mean nothing when the site goes down. While one might frown upon the idea of people helping others only for "internet points", it's actually a huge draw an effective psychological strategy that keeps probably more than 50% of users coming back to these sites.