Nullable ToString()

No, you're correct, the shorter version is the same as what other folks have done in that regard. The other construct I tend to use a lot instead of the ternary with nullables is the null coalescing operator,. which also protects you from nulls. For ToString() it's not necessary (as you pointed out) but for default int values (for example) it works nicely, e.g.:

int page = currentPage ?? 1;

that lets you do all the integer operations on page w/o first explicitly null checking and calling for the value in currentPage (where currentPage is an int? perhaps passed as a param)

I think that many people have such checks because it is not a natural behavior of an object that can hold null value.

You are quite correct. Also in this question, the former solution is suggested while nobody actually notices ToString() already gives the correct answer.

Maybe the argument for the more verbose solution is readability: When you call ToString() on something that is supposed to be null, you usually expect a NullReferenceException, although here it isn't thrown.