To be fair, swiping is fairly common in iOS apps. Mail and Reeder come to mind. When I try out a new app I usually test to see if UI elements support gestures like these.
Showing some kind of button defeats the utility somewhat, and I think a help pane explaining available gestures would be a better solution. You could stick it in the preferences view.
I agree with you that we've trained users to expect UITableView Cells to be swipeable, yet I'd argue that the comments on MiniHack don't fit into a "standard" UI for cells (they don't look like a table view cell from Mail and Reeder, especially since a cell can take up more than a screen of height).
As such, I wouldn't expect my users to know to swipe them. I do agree that a help pane would do the trick, but personally I would probably lean towards an AlienBlue type of indication that the "cell" is actionable (the triangle showing Compressed or Uncompressed, and a row of icons that appears when you tap the cell, instead of the popup from the bottom).
That said, a JazzHands[0] type tutorial would serve perfectly fine too!
Showing some kind of button defeats the utility somewhat, and I think a help pane explaining available gestures would be a better solution. You could stick it in the preferences view.