Most people play Dota2 because they want to play Dota2. They want to play. And SOME, only SOME of those 10m users expand their interest beyond playing the game. I'm talking about the people who are actually interested in the workshop. That's a really small portion from the whole player community, keep that in mind. Adding…
Do not confuse the store and workshop. Yet they serve different purposes and the aim of the workshop to show & vote and not selling! For sale we have dota2.com/store - and for advertising Valve use your Promo art I don't propose to abandon it.
On somewhat related note, I just noticed this : http://www.dota2.com/store/itemdetails/20684?r=c9 http://cdn.dota2.com/apps/dota2/images/store/arcana20684_mv0.webm So basically, there is now a new kind of preview ! And since it's just a video, it's available from the web browser version of the store too.