BEFORE:
<?php print $content ?>
<?php print $sidebar_left ?>
AFTER: {$content} {$sidebar_left}
I, personally, see no rationale in a theming markup language. There is very little point in saying "I know you don't understand { or } but use it to encase this dollar-sign word" when the exact same mentality is required for "I know you don't understand <?php print or ?> but use it to encase this dollar-sign word".
For the same reason, I have similar complaints about wiki markup (memorize _ as opposed to the far more useful everywhere <em>) and bbcode systems (memorize [url=][/url] as opposed to the far more useful everywhere <a href=></a>).
If we're going to force people to memorize something, let's force them to memorize something *useful* and which has a semblance of repeat knowledge and value at other sites and software they may use.