Yes, yes, the famous hosting environment argument. It comes up whenever the WP team just don't want to do work on the actual guts of the system as opposed to tickbox features.
When they added autoupdate, that had large host environment implications. Import/export has host environment implications. It goes on and on.
There's no technical reason they can't have a simple page cache in mainline that turns itself off when there's no write access.
Not to mention that WordPress is now popular enough to bully hosting companies if they wished to do so. What hosting company would want to admit that their services are incompatible with the latest version of WordPress? WordPress is no longer under any realistic obligation to respect the lowest common denominator of hosting environments, because whatever it requires will become the norm. It's a trememdous power that few open-source projects enjoy, and one that could be used for the greater good. If the next version of WordPress just went ahead and required PHP 5.4, for example, the hosting industry would have no choice but to upgrade their PHP versions a.s.a.p.
http://codex.wordpress.org/Class_Reference/WP_Object_Cache#P...
On the other hand, as of my understanding Drupal does page caching to DB by default (straight out of the box?) and seems super quick.