It may not be supported by the latest OS 10.9.x but it is still supported by Lion 10.7.x and Lion is still getting OS updates from Apple. So you are still supported. Eventually that will change once they release Yosemite in the next few months. Apple generally doesn't support more than a couple versions back... basically to cover their 3yr. Apple Care extended warranty. That combined with their OS versions gives you around 5 years minimum of support. While not ideal... it's not too bad.
I also think the hardware support will lengthen as most don't need much more power to email, browse, watch videos, etc. OS versions will probably support older and older hardware, unless some new feature comes along that needs more processing power (better language processing?). My Mac Mini (Early 2009) it will be supported with Yosemite 10.10... which means even if that's the latest it can support... it will end up with minimum of ~8years of support. I think that is pretty good.
Disclaimer: I work for MIT OpenCourseWare and still get annoyed that we have a ton of people who don't know about us cranking away at free course materials for the world for more than a decade! (MIT OpenCourseWare was announced in 2001.)
Who will now take the responsibility of culling the herd?
MIT OpenCourseWare (https://archive.org/details/mit_ocw) stores a copy of all the videos on its site on the Internet Archive. Currently that is 75 full video lecture courses and 17 full audio lectures courses, plus a ton of smaller one-offs and mini-series video and audio files. Over a thousand hours of teaching. I would like to think that would be something of use to the human race.