kohoutek, can you explain how you know the "default unit" for WIDTH is pixels?
Let's say for example you have as follows: <img src="..." alt="..." /> the IMG is an empty 'replaced element' thus would not have a "default unit" for a "width".
If anything it would be a percentage (%) width if I understand it correctly and not actually pixel units.
I assume you meant if the IMG had a WIDTH attribute omitted and no CSS was involved that you believe it would be replaced by "pixel units", which I cannot see is the case.
Or do you actually mean the actual image SRC file let's say 'sample.png' would "default override" and force the issue.
Otherwise I cannot see how it has a default unit in the absence of either CSS or an explicit 'width' value, i.e. ="100" or "100%" .
If I 'misunderstood/misread' your answer; then that's fine.