I agree that the dell 27" will be of a lower quality than their smaller and larger units. I believe the reason they announced the price of the 27" is they too, believe that apple will come out with a TBD in the next few weeks. It may likely have a bump in resolution, but not 4K. They want people to compare the other size dells and decide if they should wait a month to get true 4K over the apple. That's when we will have more of a choice.
Most people on here are comparing next months dell, with the old current TBD. The Apple product will likely come out sooner. Apple went out of its way to tell us the Pro could be hooked up to 3rd Party 4k monitors. When you compare a heavily outdated product like the current TBD, considering apple doesn't reduce prices over a product's lifetime, of course it is now a horrible deal. When the TBD came out, it was a great deal for a great monitor and hub.
In a couple weeks, we will have a stealthier matte screen with an up-to-date hub and it will again be a great deal considering the functionality, ease of use, and sleek look. It won't be a 4K since apple won't go with 4k until they can do a great panel at a reasonable price. Dell builds monitors of all different quality. I'll bet next month's dell 4k panel will not be up to apple's standards. Then people will truly have a choice.
If you're a laptop user, a hub/monitor is a nice addition. If you have a desktop, it's too much for just a monitor. Sure the apple tax is a lot for the current TBD, but in a few weeks, that tax may even be nonexistent. All things then being equal, I'd prefer the elegant design, superior manufacturing AND function of the apple. Two cables to connect everything you need at home to your laptop is more than beauty that's just skin deep.
I agree the faithful will buy overpriced outdated products like the current TBD, which then I agree with going the dell route. Once the new one hits the stores, it will be the best product at the best bang-for-the-buck for a lot of apple laptop owners that can't drive a 4k display anyway. Having the high resale of Apple products allows users to upgrade easier as well.
For me, the decision between dell and apple is more of a question of how recent the release is in it's life cycle, quality of panel, and wether it's connected to a laptop or desktop. I think either extreme, in all cases choose apple or in all cases choose dell are odd stances to take. I'm glad we all benefit from competition, and can buy the best choice for our own situation.