The Mac Pro is a significant redesign, but not a new product line.
Apple has often (in recent years) been in a position where significant portions of their revenue are from product categories which did not exist 2 years ago. There is a fear that they will not continue to invent/expand into new categories.
Any new product category didn't exist 1 day ago when it's launched, but we don't expect new product categories every day. In the 15 yars since Jobs re-joined apple to the time he died he's credited with introducing three new product categories: iPods, iPhones and iPads. Arguably iPads are actually just a scaled up iPod Touch and nobody ever lists the touch as a new category. From a technology point of view it was a modest revision of an existing product.
So personally I'd list the new product categories as only two - the iPod and iOS. It's just that iOS' revolutionary impact hasn't completely played out yet. I expect any new 'product categories' to be further extensions of the iOS family into new markets. e.g. Apple TV is an existing product running iOS, but if it grows an app store and games ecosystem, will that make it an entry into a new category?
You're right that the Mac Pro is an existing product line, but it's so radically different from it's predecessors that I do think it has a chance of being used in ways and contexts the old Pro never was. For starters it's tiny. It's agressive use of Thunderbolt is interesting, but also the emphasis on GPU utilisation via CUDA and OpenCL - one of it's GPUs isn't even wired up to be used to drive displays - is a bold move.
I don't know. MP3 players, smartphones and tablets already existed for a while by the time Apple announced it's products. But the products were so successful that they are now credited as having (re)invented the market. I don't see why this can't happen, for instance, with workstations, this market has been stagnant for a while.
Looking at the MacBook Air, and retina MBP, and their success, Apple seems to have done a fair job of reinventing the laptop market. Quite possibly, the desktop will follow.
Apple didn't necessarily invent new categories, they offered revolutionary products in existing categories. Even back from the start. Mac (obseletes CLI) iMac, iPod, iPhone
If only Apple would make the Terminal.app user interface not suck donkey balls. How about a way to resize the property window profile title scrolling list width so it doesn't clip every title after the first few characters and make them extremely difficult to identify and edit, and stop wasting so much of the width on a huge useless icon instead of the title? Is it so hard to make the whole dialog resizable? Didn't Apple invent a way to do that a few years back? Oh and maybe a fucking border around the window edge so overlapping windows don't all merge together? And a way to drag a window with only one tab (which collapses to zero tabs) into another window with only one tab to make one window with two tabs? And figure out why emacs gets confused about the screen width/wrapping and corrupts the display? Maybe fix a few critical usability bugs before wasting time on bullshit like transparency and background images?
...Well at least it's not as bad as the XView cmdtool.
Apple will continue to expand into new categories it thinks will do well. They're traditionally concerned with a product either being the market leader in terms of quality, rather than being the inventor of a category.
Plus this whole inventing new categories things is silly, you'd have to go back a long way for Apple to have created a category, they excel at being more refined than existing players.
Apple has often (in recent years) been in a position where significant portions of their revenue are from product categories which did not exist 2 years ago. There is a fear that they will not continue to invent/expand into new categories.