It's not just about being decimal or hexadecimal, since "1_1" == 1_1 is false (thanks haukex for mentioning the digit separator). I'm not sure if this is enough of a reason, but obtaining the same value with or without the quotes only works when you can stringify and turn into a number (numberify?) back and forth without changing either the string or the number. For example you wouldn't obtain the original string in map { "$_" } map { 0+$_ } "0x16"; if "0x16" was interpreted as 22.

Now "Don't use a string as a number if the number won't give you the same string" could have been a pretty good safety net, if perl didn't allow some oddities like "4 ever" being interpreted as the number 4. And print "equal" if '12.9999999999999999' == 13 prints "equal" on my version of perl.

Edit: you don't get your original string either with leading 0. print "Different" if "042" ne 0+"042";. "042" is 42 but 042 is 34, so once again if "042" had the same numeric value as a bare 042, it wouldn't stringify back to the original string.