That is not true. Dilbit is now worse than light oil spills depending on the sea conditions and the clean-up response.

http://oils.gpa.unep.org/facts/fate.htm

Also, a recent Government of Canada study has shown the dilbit floats on freshwater.

http://www.financialpost.com/m/wp/executive/blog.html?b=business.financialpost.com/news/energy/study-showing-that-spilled-oilsands-crude-floats-on-fresh-water-could-help-unlock-stalled-pipelines

Also, dilbit is currently being shipped in batches on the existing Transmountain pipeline. Future mining production will see paraffinic froth treatment dilbit with an API of 18 or so. Read up on it. It is a cleaner refinery ready product than napthenic bilbit (cut with condensate).

And finally, even if 'refining' it in Alberta were economic, Alberta's GHG emissions would really escalate and effectively double the overall GHG count because it would be upgraded and then refined at destination.