Better late than never...
I don't pretend to know all the ballast types sold in North America, but here in 220-240 V countries by far the most common are the magnetic ballast + starter ("preheat start") or the electronic ballast (HF).
Because of their simplicity, the magnetic ballast will be around in sheer numbers.
When installing LED-tubes, for best efficiency, it should be removed or bypassed, so that the LED tube runs straight from the mains. So yes, an LED-tube is just like any other LED lamp operating directly on mains voltages in that it has an LED-driver converting mains to a suitable DC voltage.
But the fluorescent ballast may not be easy to reach inside most luminaires making conversion time consuming. So for ease of conversion (especially for non techies or big jobs) they can be left in place and a dummy starter takes the place of the fluorescent starter. That dummy starter is just a short circuit. The ballast basically is degraded to being a conductor.
E.g. this Philips tube's name implies the use on mains or magnetic ballast:
MASTER LEDtube EM/Mains.
I'm not familiar with "instant start" or "rapid start" ballasts. But what I read in this
Wikipedia article is that the former forces a tube on by sheer high voltage (the tubes have only one pin on either side) and the latter by separate windings and an grouding strip applied on the outside of the tube to aid strike an arc. I guess neither of these two types would be really suitable to be left in place when an LED tube is installed.
There are also LED tubes that are supposed to work off some of the electronic ballasts as well (the Philips tubes suitable for that seem to have "HF" in the name (e.g.
MASTER LEDtube InstantFit HF T8), for the same reason as above, however, compatibility may be more of an issue.