It's that supposed to be an argument against HTML emails? That some companies choose not to implement it for compatibility? Like, let's stop printing because companies are making proprietary cartridges and breaking compatibility??
Instead of using floats and margins, you have to revert to using <table> for layouts. Otherwise, your emails just won't render correctly, much of the time.
It's not possible to support HTML fully in Webmail clients, either. Even without scripting, you could write an HTML email that overlays a malicious button on top of Gmail's web interface itself, and it would be too easy to phish people.