An alternate construct could be something like:
""" def While(x): if x > 10: return None else: return x
[w for w in (While(x) for x in range(20)) if w is not None] """
The problem is that this version won't work if range(20) is replaced with itertools.count() or any other non-finite generator, whereas the raise Break version will.
Another nice thing about using raise for loop control is that "raise Continue" can be used to skip elements:
def even(x): if x % 2: raise Continue else: return x
[even(x) for x in range(10)] # [0, 2, 4, 6, 8]
This would have to be broken in two parts to do in current Python (and indeed, that might be the chief advantage of *not* adopting my proposal--TOOWTDI):
def even(x): return not x % 2
[x for x in range(10) if even(x)]
As for beginners in Python, I don't think learning to use "raise Continue" instead of "continue" will really be that hard. I think the main reason to reject my proposal is that complicated loops shouldn't be done in list comprehensions at all. They should be written out, like reduce expressions. Still, it might be convenient in some cases, and it would be a good chance to cut out unnecessary keywords.