Few questions:
A. How come only 14 eps?
B. How come no third season?
C. Did this show run weekly or monthly or?
In the UK its not uncommon for a show's season to only have 6-7 episodes, hence the lack of episodes for Spaced. Them 14 make up 2 series as I'm sure you know. The show aired weekly, i think it was on a Thursday for series 1 and a Friday for series 2, but I'm not 100% on that.
There was never a third season because Simon and Jessica went off to do other things, and as they did more and more, it got less and less likely that a third one would be made. They always used to say that they would like to do another when they have the time, but more recently they've taken to saying that it's not likely. Personally i think it was never even considered, as to me the ending was perfect as it is. If the US version has the documentary included, then theres a little 'ending' tidbit on there for you.