I was not aware that this basically meant each individual uploaded file (embedded to an HTML file) is scanned before hand and checked to see if the selected file is below 20mb. If it is below 20mb, the PS Vita will download via 3G. If the file is above 20mb, it will not download via 3G and 'only Wi-fi only download' notice might pop up (or w/e the equivalent is). This is on the NTT Docomo plan for the 3G+Wi-fi vita which offers hourly plans at 128 kbps download for 20 or 100 hours (the 100 hour plan can do a full 14 mbps and 5.7 mbps for 3 hours).
Where are you getting this "information"? I couldn't find any mention of it from the link you provided.
That's because it doesn't scan file embedded in an HTML page. It pertains to things downloaded thru the store and such. Web browsing and gaming are not influenced by this. The device (the Vita) determines when a file is to large to download. Your wireless provider does nothing. They just announce the limit to the device when it's activated.
It said "just like Apple with the iPhbe and iPad" which is exactly what I'd expect. I can't download a 20MB podcast from my phone via 3G... but I can stream that exact same podcast instead using 3G. Same amount of data... just sent over a longer period of time.
I get the impression also you beleive that you are forced to always use 3G on files smaller than 20MB and WiFi on file larger then 20MB. THIS IS NOT THE CASE,
Wow how do these things get started?