2. Why did it "fix" the bad sectors on my deathstar before the physical damage became too great for it?
You don't really "fix" bad sectors. As I understand it, what happens is if there is a verify error somewhere, that location gets marked as a "bad sector", and then the drive continues on it's merry way. You can go back through and use a program to remove the list of marked "bad sectors", and viola, you've got no more bad sectors listed. You've "fixed" the bad sectors. (Of course, you haven't fixed anything, and when those sectors are used again, they'll probably get a verify error again, and get marked as bad again, etc...)
As for general drive quality... I've never had a problem witn any brand in particular, with the possible exceptions of Maxtor and IBM. What is much more important is mounting and care.
1) Drives need to be mounted firmly so they can't vibrate.
2) Drives need to be mounted level so they can spin properly.
3) Drives need to be protected from rapid changes in temperature while in operation.
4) Drives shouldn't be operated in extreme heat.
5) Drives need to be protected from outside shock and impact.
Following these five simple rules, pretty much any hard drive should live quite a long life. There are, of course, exceptions, but even those are usually less severe. I had a Maxtor croak on me, but it gave some warning time, so I was able to easily ghost the drive image onto a new HD before it totally failed. I only suffered about a half-hour of downtime.
