Why reinvent the wheel when you can use one known framework(e.g. blueprint) than will be instantly recognized by other designers?
Secondly, this is a poor analogy because we're talking about 3 CSS classes- by no means a "wheel". I am curious as to what circumstances you would really save any measurable time using a CSS framework.
Some designers however seem to use divs for tables and it just looks silly and ends up being overly complicated.