Only during preview.
I haven't found that to be true. Maybe I've been doing something incorrect somewhere? If that's actually suppose to be a feature, then I suppose I'll submit it as a bug report.
Example (capx):
As you can see, the power-of-two sized sprites move/look smoother and with less pixel jitter. Without being that square size, it seems as if it's doing "point" sampling rather than "linear"!
Anyway, I hope WebGL 2 won't take too many years, so we can get this one improvement!