The USB loader came out and quite simply it's useless for anything besides backing up game saves and small emmulators that can be stored in RAM. If the PS2 did use USB2.0 ports it would just be a waste as nothing they've developed (headphones/mic, eyetoy, keyboard, etc.) actually need it. The ports do exactly what they need them to do and to upgrade to 2.0 and release new peripherals would just hurt the millions of people with USB1.1 slots on their old original systems, who werent going to upgrade to a PStwo.
Unless they develop some sort of pass through for the Ethernet adaptor or something, there's no HD support for the PStwo.
The problem is Sony didn't want to bother with the HD after the second year of the PS2s life. Their whole hope was to be able to sell online sevices like movies and music, but abandoned the idea when the cost of setting up the service was matched up against the predicted userbase for it, plus there just werent enough Boradband users to build an inferstucture of the size they wanted yet. It was used a lot more in japan but with sony's reluctance to spend the money on it here, Square-Enix who'd put a lot of money into FF11 had to lobby hard for it's eventual release here and put up much of the money (this is probably why they're still making the effort to make compatible games for it.) Lets face it the biggest use of the HD would be the Final Fantasy11 franchaise and an MMORPG at that. A genre which rarely measures it's success in millions wasn't going to do much for Sony's forecasts. So of course many of the other companies that were actually using it in japan removed HDD functionality from the games they brought here because Sony had taken so long to import the HDD, but since so many of these games seemed to work fine without it (aside from long loading times) it wasn't a big deal to Sony anymore, and they were only concerned only with staying number one in regular console games leaving Squeenix to take the hit in the wallet for the HD.
Sony eventually decided that they'd sold millions of original style PS2s and with the slow acceptance of the device by developers (despite Capcom's attempt to push it with the online Resident evil game) that if someone out there cared for the HDD and the slow trickle of games that used it, they likely would already have a version of the system that could comodate it.
So basically there may still be one or two games a year that use it before the end of the PS2 life cycle but it's not really a concern to Sony since it wasnt doing much for their bottom line anyway.