Hi joemich, welcome.
It was my understanding that fingering on all pennywhistles is the same;
Yes, that's basically right. You'll find some minor variations - C-natural, vented D, 3rd octave notes. Otherwise the basic diatonic fingerings are universal.
You're probably looking at Thom Larson's page here:http://www.thewhistleshop.com/catalog/w ... dublin.htm
The upper chart are the bog-standard diatonic fingerings.
The lower chart are the chromatic fingerings (sharps and flats) - where preference is given to cross-fingerings instead of half-holing whenever possible. Those cross-fingerings are also fairly standard and will work on many whistles besides Susatos - including Clarkes. But there are usually several fingering options for a particular note on a particular whistle, besides what is shown on the Susato chart, and it's worth experimenting to find the ones that work best. This is part of what any good whistle player does in preparing to play a given whistle.
The Clarke chart, on the other hand, gives only half-hole fingerings for the chromatic notes. That's the difference that you see. Of course, half-hole fingerings can be used on any whistle as well.
So put the two charts together, and you have the (more) complete picture.