Sounds arbitrary. And probably a security concern over a webpage causing your computer to DoS a million sites? I don't see why it would eat the battery to have the same amount of data sent over 400 connections rather than 200, and, well, battery is not a concern for desktop computers, while phone apps don't run on browsers (I imagine even the webview-wrapped apps may not be subject to that limit). Not ideal, but I guess you can add a relay picking algorithm that favors hubs over non-hubs when running in a browser.

Now assuming you have that, is there a reason why you wouldn't open 100 subscriptions on the same relay with one key each instead of a single subscription with 100 pubkeys?