Why does Mail.app mime parsing suck?

Since I write web applications related to e-mail processing, I am amazed that a company like Apple has not addressed the way Mail.app parsing sucks in Mac OS X Tiger.

handles simple messages, like mime/multipart, plain text or rich messages, just fine.

Where ti falls apart is on mailing lists, where complex mime structures lurk, such as multipart/digest or message/rfc822 messages.

The visual symptoms are that individual message parts in these complex types don’t appear correctly in the viewer in Mail.app, bleeding together without displaying even minimal headers, like To, From or the Subject.

Does their parsing code truly suck, or is this a symptom of moving to WebKit to display messages in Mail.app?

Either way, it need to be fixed.

parsing may be better, but I don't care for the aged appearance their rendering engine provides. The default fonts, aliasing and general layout is so 1999, IMHO.