Is it a good idea that Signatures are put into the message in 'real-time'? Why isn't the signature embeded into the message when you post it?

I could post a 1000 message on this board, and then with a few clicks change my signature to include some nice piece of advertising and bang all my posts are changed! That's the extreme line...

I dunno. Just wondered really why has it been built in this way? Why not embed the signature into the message?

Just thought what the idea was behind that?

Thanks

- wil