Worrying about micro-optimizations (like making sure the size of your code is <= 1.44mb) takes time away from worrying about more important issues.
"Oh no, our application can't be simultaneously downloaded by 3 million martians because our client is too big." I'm being facetious, of course, but I think the point applies. Don't build stuff with weird contingencies in mind. The average user (of an HTML5 app) will not have to worry about processing power, bandwidth, or client size. As long as it's not like 20mb or something stupid.
And, obviously, websites are accessed from all kinds of connections. Not everyone has a generous 3G plan, and even the US doesn't rank that well in average broadband speeds.
Anything you don't have a limit for will become a problem. I don't care how fast computers are, or how much memory they have, or whether you have fibre-optic broadband. If you treat the resources in question like they're infinite, you'll find out the hard way that they most definitely are not. And that's so silly, when you can just set a reasonable limit that guarantees you won't have any problems, and then... not have any problems.
Realistic limits aren't so hard to stick to if they're there, and enforced, right from the start.