Hello,
yes, support for Microsoft technologies is a very tricky topic.
I suppose all HQ developers are using Linux or OS X, all of them understand
Apache,
MySQL and
PostgreSQL. Most large installations are using Linux + Apache + MySQL/PostgreSQL (I personally consider PosgreSQL the best choice, forget
Oracle).
In order to get first class support for IIS/
MSSQL you would need to force half of core developers to use/learn MS products and somebody would have to buy necessary licenses for all Windows versions and MSSQL for all developers. Then there is also the need for necessary test hardware. Also all senior developers and integrators would have to study the IIS and MSSQL in great detail to detect all problems during integration.
The current policy is to not intentionally break things for IIS and MSSQL, if somebody finds a problem and creates a patch it is usually accepted (the requirement is that it must not break other systems).
The installation and administration documentation is yet another topic, core developers do not know how to manage IIS or MSSQL - people that want to use these systems and have the know-how should ideally write and maintain it.
Contrib plugins may have even more problems with MSSQL or Oracle databases, you have to the testing yourself before deployment.
Before my MSDN dev license expired I played a bit with the new MS installer for PHP and I was very positively surprised - the installation is a lot easier, recent PHP versions seem to work much better. The new MSSQL driver looks like a major improvement compared to the older PHP extension too.
To sum it up: I believe MS technologies are not bad, but most Moodle developers do not know enough about them (fighting with Internet Explorer incompatibilities takes tons of our time already) and they do not have necessary licenses.
Petr