There are basically two reasons to go with a .Net or J2EE solution

1. You have expertise in those architectures that you do not have in the 4GL languages, like Perl or Python.
2. You are already seriously committed to a Win32 architecture.
3. You already have a large codebase in those architectures.

For a completely new project, it often makes more sense to build it in Perl/PHP. Reasons?

1. Perl is developed faster
2. 90% of every Perl application has already been written, tested, and deployed.
3. Perl is supported on (nearly) every single system known to man
4. Perl has support for (nearly) every single data store known to man

As for the multi-tiered stuff ... I worked on an e-commerce site that had all the MVC architecture built. Oracle was on its own server, separate from the Apache servers. It was all in Perl.

I've also worked on another web app that had 4 front-end servers, using MySQL for session information. They communicated using Tuxedo across the DMZ to an Oracle server (with HA backup). All the SQL was in Pro*C in a bunch of C++ classes.

The point here is that Perl is a very effective language for every part of the web app. I've heard of apps that have their engine in Perl and use Java/.Net for the presentation layer. No problem!