I'm surprised it wasn't just "and all vowels" with the same reasoning, or at least 'a' (because I can more readily think of examples than for, say, 'e').
I suppose, though, there's an attraction in using b32 rather than b29... (Though I notice mid-word apostrophes are double-tap-selectable at least on macOS, so perhaps swapping 'a' for ''' would be advantageous, if more complicated to explain.)
I find it interesting that you're willing to say "twat" but not "bastard". I admit that I didn't think of either of those words, though I think they're still much tamer than the ones with "u" in them. Really what I was thinking of was "crap" and "damn".
I suppose, though, there's an attraction in using b32 rather than b29... (Though I notice mid-word apostrophes are double-tap-selectable at least on macOS, so perhaps swapping 'a' for ''' would be advantageous, if more complicated to explain.)