Let me provide a little insight into all of this as a professional 3D artist. First, those saying things like "tower are relics", "you can do it all on an iMac if they change some features", "who needs that much power?", etc. simply do not understand and sound like they have very little computer knowledge at all. Second, I hope like others they do not discontinue it due to my work, if they do then I will be forced to move on to Windows 7/8 fully.
As I said above, I wanted to post some insight about the segment that a Mac Pro sells to and what most use them for. For me, it is a MUST to have at least 1 or more Mac Pro computers with the most high-end features you can get. The reason is because I am a 3D artist and use programs that cost several thousand dollars each, such as Maya, Vue, C4D, etc. These programs cost as much or sometimes a LOT more than many will ever spend on their computers alone. For people like me, I am NOT and never will be a "typical" computer user/consumer. I must have at least 16-24GB of memory, a full 64bit OS and at least 2 CPUs with 8-12 cores at minimum.
Programs like that mentioned above will take advantage of just about all you can throw at them. It means not only can I render scenes faster, but I can also be more creative in my art for building a scene. With faster processors, more cores, more memory, etc. I can put say 8 very high-resolution models in a scene that are really eat a lot of power, whereas if I was limited to an iMac maxed out it would be about 3-4 models at best. Also, things would take much longer to render and produce from start to finish. That means both time and money.
Not only is a Mac Pro essential for me, but Apple has really dropped the ball and I wish they would decide one way or the other to either FULLY support it or give it up. One area that matters a lot is the fact I need nVidia cards in them for their "CUDA" cores since some high-end software take better advantage of those compared to AMD Radeon. Not only is one Mac Pro used in my workflow, but I have two others running as part of my "render farm" that is used for distributed network rendering nodes. Typically, I work from the most current high-end Mac Pro I have, then farm the jobs to the others on the network render farm. If the scene is complex or very detailed, I use all 3 of them together.
Now, try telling this to Apple. While many still complain about the Mac Pro costing $4,000+, I call this cheap. A lot will never use anywhere close to the type of power I need or features, but for those of us out there that do, it will be the end of our Apple computer purchases and be forced to Windows where we can build systems anyway we want them. So the question becomes, are there enough of us left that spends $6-10K per computer for Apple to keep the Mac Pro line going? So far it seems like the answer to that has already been given due to the serious lack of updates the Mac Pro line has seen on a timely basis. All I am pointing out is that while people like myself are not anywhere close to the "normal" computer buyer that Apple loves, there is still a market there. But it is long pass time Apple decides if it wants in or out so we will know where to go for our future needs.