Assume that I did load jQuery via Modernizr. Then what happens if someone activates both your plugin, and my plugin? Might we then load jQuery, twice? (Perhaps we'd load jQuery 1.7.2 once via require.js and once via Modernizr? I don't know how these script loaders work, internally.)
I guess that if you load only stuff that you really really know is specific to your plugin only, then you'll be fine.
(Danger: This is my first WordPress plugin and I don't know WordPress or PHP well.)