The <!-- ... --> is a comment declaration in SGML, and is able to span
multiple lines. The limitation you are complaining about is due to the
limitations in browsers to properly parse comment declarations.
A comment declaration is only terminated when the sequence "-->" occurs
(whitespace is allowed between the "--" and ">"). Therefore, you
can (should be able to) comment HTML markup; e.g.
<!--
<h2>Commented out head 2</h2>
Commented out text.
<p>
-->
But until browsers do things properly, you are limited to the "tedious"
way.
--ewh