I don't develop phonegap apps but I'll have a go at answering this:

> I'm still confused why this matters if you are packaging your assets with the phonegap build which I would expect most people do.

Ignoring download time, loading, parsing, and evaluating 250k of javascript is not free[1].

[1] http://carlos.bueno.org/2010/02/measuring-javascript-parse-a...

That article is on a desktop (well, laptop) processor. The timings on mobile are obviously higher. JS parse & load is mostly ignored on the desktop but I know I've read at least one article where a team was pulling down their JS as plain text and eval()ing it later to get their load times down.