That's fair, and true from an engineering perspective. I imagine for YC it comes down to, as with nearly every other company, a prioritization problem.

With the exception of companies like FB with millions of users, the priority of creating a css/html rendered version of text to prevent people from having to click through to copy is quite low.

I suppose I'm defending the image as being the more useful of the two "easy way outs" that are likely to be implemented. :)