There's a size limit on attachments - everyone will have their own idea of size and resolution - so some cameras may produce 50KB pics, others 10MB pics. Soon we'd run out of disc space or have to pay for lots more storage, worse we could go round deleting old posts and pics, but lots of them are there to help other builders or explain things.
In short, there's a limit and for the moment thats it. If you wish to post larger pics / higher res then you can always include a link to a pic hosted on your "own" web site - that's what some of the posters have done.
Sorry, I do realise that it's a pain having to resize / scale the photos before posting - the limit even applies to me!
- tenpin