A question upvote here gives user 10 rep, but on other metas it's 5. Why so?
[update] Apparently, upvotes on per-site metas don't gain one any reputation. So misleading. All this time I thought...
Because this meta is special.
Prior to the launch of the SE 2.0 sites (Web Applications etc.) there was only this meta site for Stack Overflow, Server Fault and Super User. With the expansion of sites it was decided that each site would have it's own meta. As part of this change it was decided that the meta would inherit the reputation from the parent site.
However, as this site was a fully fledged site with it's own reputation and because it's a place where questions about the whole network are asked it was decided that it would keep it's own separate reputation. To quote Jeff from the blog post I linked to:
The second-last paragraph of ChrisF's answer is the rationale. :)
This site deals with the SE network in general so it's ill-fitting to have SO's rep carry over. Being an SO user with high rep doesn't make one qualified to comment on things for the English.SE site, for example.
At the same time, having high rep on English.SE very much means that the person is likely qualified to comment on the direction of English.SE, so their rep carries weight on English.SE meta.
In a way, you can think of StackOverflow meta as a separate StackExchange network site with its own rep.