I really agree with your first point. There is an incredible amount of potential in web pages as teaching tools. I'd love to see someone make a math notebook environment for tablets with a stylus. It could pull up a sort of intellisense as you write (for example first, second, nth derivatives, common expressions, suggestions for factoring, etc.). It could have graphs. It could have a reddit like QA section. Really, there are so many unexplored ways of connecting people who are struggling with a concept with just the information they need. Who wants to watch a ten minute video to hear about that one equation three quarters of the way through? Just learn what helps people like them and offer it up as potential solutions while they are working through problems.

There is the possibility of pre-endering Mathjax but that seems like it would be a lot of work.

Why do images suck balls?

What’s wrong with just inserting a URL with parms that generates the image on the fly and changes at needed?

For example, analogous to image processing services like. http://www.picresize.com

The most obvious reason is that they don't work well from a copy & paste perspective. They also don't naturally fit in with the page's normal reflow / line-breaking logic, so they can look awkward and out of place depending. Your solution works to a point, but it complicates things.

Don't get me wrong... using images for equations is better than not having equations at all. But personally I consider that approach quite inferior to native MathML rendering.