Majority of websites can be converted to 5 just by replacing doctype. Nonstandard attributed don't help you to save bytes though. Also, from what I've seen site

Majority of websites can be converted to 5 just by replacing doctype. Nonstandard attributed don't help you to save bytes though. Also, from what I've seen sites which were built without even thought about validity and standards tend to be of much lover quality and hence are more bloated: lots of unnecessary div's, classes, wrappers, etc.