Any caveats in using unpack to right-trim?

There are two:

• It doesn't remove non-ASCII whitespace characters.

  $ perl -Mv5.14 -e'say length "a\xA0" =~ s/\s+\z//r'
  1
  
  $ perl -Mv5.14 -e'say length unpack "A*", "a\xA0"'
  2
  [download]

• It removes NUL.

  $ perl -Mv5.14 -e'say length "a\x00" =~ s/\s+\z//r'
  2
  
  $ perl -Mv5.14 -e'say length unpack "A*", "a\x00"'
  1
  [download]

I've been unsatisfied with the speed and came with "better" version.

Why doesn't builtin offer this???