Oh wait! It doesn't show up when using the App Store app!
So even if you put a link there you need someone to be aware that such a link exists, to believe there might be something useful at the end of that link (which you point out, there rarely is), then wants to go to/turn on their computer, fire up iTunes, attempt to & succeed at finding your app, click the link, possibly register for your bug tracker (doesn't seem too uncommon), possibly check their email to confirm their registration and then finally file a bug report.
So even if you put a link there you need someone to be aware that such a link exists, to believe there might be something useful at the end of that link (which you point out, there rarely is), then wants to go to/turn on their computer, fire up iTunes, attempt to & succeed at finding your app, click the link, possibly register for your bug tracker (doesn't seem too uncommon), possibly check their email to confirm their registration and then finally file a bug report.