It's a 30% cut for using Apple's distribution channel. And no Apple doesn't let app developers use the channel whilst telling their users how to bypass the 30% cut.
Just like I can't go to any retail store today and on any of the clothes or boxes find a giant sticker that says "buy this product on our website for 20% cheaper". No retailer would tolerate that.
You'd have to add that it's more like you own a car that will only take you to that one store.
Even the dodgy ones on eBay seem to be 10% off max, and I'm fairly sure those are primarily used for money laundering and/or credit card fraud.
Yes, but like with any other purchase, you have to get it from a reputable retailer.
I usually load up at brick-and-mortar places on Black Friday weekend and then use them the rest of the year.