You are incorrect--50% of the ISS's needs are being serviced by the Soyuz-TMA since the ISS program began--it seems you're just biased towards the American space program part of the ISS

The Russians have contributed a LOT. In fact I bet you didn't know that the current ISS escape system (i.e. emergency escape vehicle) is actually a Soyuz-TMA docked into one of its many modules.
Soyuz-TMA - Wikipedia, the free encyclopedia
The next vehicle slated to serve the 50% missing services now that the shuttle is getting retired is none other than Elon Musk's Dragon...
Dragon (spacecraft) - Wikipedia, the free encyclopedia
-RODION