True, but it would be nice to augment Mutt with things like tags and conversations[1] without having convoluted setups involving hacks with external scripts.
Another example, it would be really cool to be able to edit email as Markdown/Textile/reStructuredText and have it converted to a text+html (multipart/alternative) email, but currently there is no way to do that with Mutt without using some sort of sendmail wrapper that does this.
[1] I realize that Gmail's threading isn't 'true' threading, but I'm talking about pulling in the entire thread even if it's not part of the current email folder.