because the original post serves as an indication of a persons attention to detail abilities and general measure of 'the person'.
the quality of a persons original post and the nature of its errors is a reflection of a persons true colors/nature, kind of in the same way that dogs and their owners often look alike.
and this forum, above all, is about honesty and transparency, thus it's important for forum members to be able to ascertain an impression of others, and the original post says it all.
additionally, the fact that you cannot edit posts encourages the development of attention to details skills and patience.. along the lines of, 'get it right the first time'.
thus, not being able to edit posts promotes skills which make for better software development... finite attention to detail skills, patience, quest for perfection, exacting precision, perseverance, etc.
not being able to edit posts is all part of the Awaresoft 'gran pan'.
