If they just returned an int, you'll sooner or later see it passed through five different places, and at the end location, nobody remembers if it's ms, time ticks, seconds, or even a unix time instead of a delta. TimeDelta removes that question.
It also does things that have subtle issues you might miss if you did it "by hand", like saturated adds, multiplying with an integer value while handling overflow correctly, etc.
These things might be overkill for smaller project, but once you have something with hundreds of contributors, every little bit helps keep the code base sane.
As for the division by 10 - look up at line 953 :)
Yes, it should be a named constant. And some of the comments could certainly be better. It's a work in progress. (And if you want to help with that work, we happily accept patches!)
