The Conde Nast magazines (Vogue, New Yorker, etc) have iOS apps in which you basically download a glorified PDF for every issue during your prescription period. I haven't done it in awhile but the PDFs are generally massive, around hundreds of megabytes, but contain full-color spreads and ads like you would see in the print product.
The problem with "tablet" magazines are that they force publishers to pick one tablet to optimize for. There is no equivalent to responsive web design in the magazine sector. So what you end up with is content originally designed for a 4:3 10" Retina iPad, but also available via the Play Store or dedicated magazine app on form factors where it has no business being, like an 8" 16:10 Android tablet, where you have to zoom, pan and scroll to see the whole page. It is enormously inconvenient, and I would guess most people just end up going to the website, which in most cases is responsive and will likely work well on a tablet, laptop or phone.
Magazines on mobile devices should offer the same level of comfort and convenience as their physical equivalent. I would love to swipe through pages like I do on my eBooks, as I find scrolling through text every few seconds to be a hassle and visually disorienting, especially for long-form reading.
I'm happy to continue to subscribe to physical editions of my favorite magazines, as the mobile experience doesn't offer nearly enough at this time to be worth my while.
I need to be convinced that tablet magazines were ever alive before I can be convinced that they aren't dead yet.