On the other hand C, Java and PHP complement each other. Whereas Python is a general purpose scripting language PHP is built for Web. It will be a huge motivation for a first year comp sci student to be able to write together a simple site in PHP and find some free host to put it in.

I think "practicality should beat purity" for an introductory course. The students usually will have a chance to catch up on Python in a data visualization class anyway.

PHP is much simpler in terms of understanding, you do not need to explain what WSGI is, what routing is, what template engines do etc. Put your code into <?php and ?> and you're all set.