While the article pertains more to the mobile game realm (my day job), I think it applies to your question too.
As for large files, well... users still need to download the HTML pages, and all the related content, which takes time and disk space in a cache. Or they can save it locally for an increase in speed, but they're still taking up all that disk space.
The one thing HTML 5 supplies is a true write-once-run-anywhere scheme. But you can get the same benefits once you have a framework written on each platform you plan to develop on. And in general, C++ is "portable" across platforms anyway.