One of the latest updates in firmware did update the browser to support Flash but only up to version 7 or so- Sony's plug in isn't exactly up to date. java still isn't supported in the PS3 browser, either, as you surmised.
Sony would have to be involved somewhat as it is their browser and you would need to know some of the specifics of it. What little browsing i have done, however, i have had no problems with it. It still is a far cry from using Firefox on the Pc, however. Until they can make it more on par with what is on computers i'll be leaving the PS3 browser alone.