This is largely a consequence of using the GPU for rendering - most of the memory is being taken up with the frame buffer and the font glyph cache. GDI based applications use a shared font glyph cache and the desktop frame buffer, so the memory usage of both isn't counted against them.
If you can't justify having an application using 50-100 megs of memory, then perhaps Sublime Text isn't for you. While I spend a great deal of time focussing on efficiency, I'm more focussed on responsiveness than memory usage. If memory usage was a primary concern, there'd be no GPU based rendering, and hence no minimap, and no embedded instance of Python, and therefore no plugins.