Zuh? Whitespace issues are generally so insignificant that if it doesn't get fixed when the code is fixed then the whitespace issues might never get revisited. They're also tedious to keep track of. And for a large patches the follow-up whitespace code review can fall out of sync with the actual code review and make resolving conflicts between the original patch and follow-up whitespace patch prone to error. And in case we have to cherrypick changes to rollback it doesn't make sense to have to worry about a separate patch for whitespace fixes.
Just my $0.02.