Pretty simply; the buyer's location is known, and Canadian sales tax rules are much simpler than US ones: the buyer's province is all that matters. They add the tax rate for that province (if any) and the Federal GST, or a blended HST if that exists for the province, or no tax if the buyer isn't in Canada.

It beats having to set a bunch of money aside and work it out yourself at year end.

Do they collect and remit the HST, or do they pass it on to you for remitting to the CRA?

Sorry, I'm not an iPhone developer, and I was always wondering how the accounting would be handled.

I'm fairly certain that since they are the 'retailer' they collect and remit the hst. What the store pays you isn't subject to hst.

What about the 30% commission?

I'm assuming they charge you HST on that which you can recover in your HST filings?

Collect and remit.