I realize that Time Machine is not SuperDuper! As Tom Yager (no relation) puts it "Time Machine is archiving, not data protection." I get that, but for most people who are going to use Time Machine as their primary means of backup, it doesn't matter--they don't care and, for the most part, that's okay. If their drive fails, they will expect their external Time Machine drive to save them. And, if everything is in order, it probably will.

One exception in the probability of this positive outcome is if they use a partition of their boot drive as their Time Machine volume, as this article explains. When (yes, when) their boot drive fails, the whole drive fails.

The article makes a good point about the usefulness of a Time Machine partition on the boot drive:

...this solution might...be useful if you simply need to recover previous versions of files or files involuntary deleted.

And also correctly warns of the inherent dangers:

backups performed by Time Machine will place heavy request on HD heads, and could lead to a shorter life cycle. (Ed. see previous comment about the inevitablity of drive failures)

I'll leave you with a quote from Jurassic Park which, for me, sums up my feelings on a large chunk of geek stunts like this one:

"...your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."