Don't the piwik team have a copyright on the name? Surely they can prevent them using the name if they have.

They have a trademark on "Piwik", not on "Piwik PRO".

Have a look at http://piwik.org/faq/new-to-piwik/#faq_21984 for a more detailed explanation.

They would usually have it (you cannot add a word to circumvent trademarks), but they sold a license to Piwik Pro. So there was no intention to avoid the naming issue, rather the opposite.

Isn't the name Piwik PRO confusing for customers of Piwik? Can I call my company Microsoft PRO? Or can I call my product Windows Pro? I at least can't call it Lindows in the USA, that's for sure.