It would be pretty naieve to extrapolate that they can't block existing firmware hacks just because they are now using physical methods to prevent new hacks from happening. The two are not related.
Look at it this way, it costs them very little to add a little glue on the board during assembly. Even if they make their holiday numbers and have 10,000,000 machines on the market by Christmas, that is only 10% of their long term sales goal. If they can easily and cheaply make it really difficult to do a firmware hack for 90% of their long term market, they would be foolish not to do it. The harder it is to do, the fewer casual users will do it -- leaving the hack only to hard-core pirates and folks who just like f'ing around with hardware. And that is a tiny percentage of the population.
On the software side, anything they do to block existing hacks is only addressing 10% of the potential market. So it is less important overall, and since it is software, is will be more prone to being overcome by more hacking. Given limited SW dev resources (Xbox is a small part of Microsoft after all), they are probably focusing on features and adding benefits for users rather than spending a ton of effort on rushing out a DVD firmware fix. Will they do it? Yes because they have to make the gesture to protect the sales of games for their partners. But it is, in the long run, less important than preventing future hacks.
I am guessing that we will find that the glue used is pretty tough to remove without queering the board, and that reflashing is now a LOT harder than before. We will probably also see a hammer come down on existing mods about the time that Gears of War comes out. Of the two, making the drive a pain in the butt to mod is more likely to have long term impact.