I really hate to defend flash, but then again most of what he brought up isn't even flash specific, it applies just as well to javascript, take Google maps for example. It does mouse hover, left click, drag, and right click to name a few. Saying you can't do flash on a tablet touchscreen because it's missing the hover etc, will also eliminate some very useful non-flash sites as well.
The N900 microbe browser address most of those. By default in the N900 press and drag will scroll the page up, down, left, or right, it doesn't pass that on to javascript as a mouse drag. The N900 has a mouse over/hover mode, swipe from the left at nearly the bottom and a pointer appears where your finger/styless is. That works as long as you keep dragging your finger around without letting up. To click, or click and drag press or hold the shift key (or space). That's enough to get around in google maps, but in agreeing with the author it's slow and awkward, I mean just trying to hold the device with your left hand and sometimes press shift while pressing and moving with your right. It's almost enough to want to find a hard surface to set the device on.
As far as I know there isn't a right or middle click, if it's there I haven't discovered it. Though, they could easily assign another two keys for them. That makes some of the google map functions unreachable. So yes, a good part of what he mentioned is supported, it's just slow to do, but so is doing about anything on such a small device. If you are wanting to play a fast action game that needs three buttons and keyboard chording, use a full sized computer, but most of it is there if a N900 is all you have at the time.