Apple is not dominating the market because of blocked sales. It's not like Galaxy Tabs were flying off the shelves. If they were Samsung and the tech blogs would be crowing about it like they are with the Galaxy S III and Nexus 7.
Quite honestly I think the Nexus 7 impacts Kindle Fire and other Android tablets more than the iPad.
The Galaxy tabs were pretty popular, they still are, the Note 10.1 will be a good sales hit.
I'm pretty sure they would impact Apple's market share (of which it is blocking competitors to keep) if they were on sale in more places.