ive always thought your amount of post up on your name was
simply by making new topics? my mates just recently come
back to using this forum but when he comments on a topic his posts
go up. has this always been the case? or is it a fault or a new thing?

yehh just im sure it only used to be on topics you make

No it never has. Hence "posts:" 

Some areas of the forum do not add to your post count such as the Chill Zone and Classifieds section so you may have only noticed post count increasing in other sections.

Veero

I'm not sure if the counter for my posts is working correct, its on about 10 but if you look in 'Show Posts', I have more like 20 that aren't in the Chill Zone or Classified Ads, most of them are in Media. Is that right?

Yeah but I've only got 3 that aren't in either the Chill Zone or Media, so some must be counting and not others.