The mac version doesn't have exact ppi control, but in our advanced preferences you can choose to scale down retina images (72 ppi), or uncheck it to leave them at their original resolution (usually 144 ppi). I hope this helps!
Thanks Luke - that's helpful as a stop-gap for now. Ultimately I need images up to 300ppi to meet requirements for pre-press and printed media type work. I'm really surprised this isn't supported on mac since that platform is pretty much de-facto standard in the design/art/printing industry - which I assume is a big demographic for your customer base.