Ok... So basically a RIP is a type of program that bypasses your printer driver and uses its own code for printing. Now, QI isn't a true RIP in that it doesn't actually use custom drivers the way Imageprint or Colorburst do, but it does ignore typical limitations imposed by Windows or Photoshop for printing either gigantic or a large number of images, so it's more of a "print manager".
To give you an example of what it can do, imagine you need to, for some reason, print 200 images. You need them all properly cropped, scaled, sharpened and printed using proper profiles and color managed. Maybe you even need a good bunch of them with light color correction. Good luck finding an application that will do all that for you in about 5 minutes of setup time.
In theory, you can do some of these things in Lightoom, which also has a fairly flexible print manager, but LR does lack some parameters for fine-tuning the print job, and most importantly, depends on the Windows print spooler, which will explode if you queue up more than a couple dozen images.
As for superior sharpening, what QI implies with that is that you don't have to worry about any image parameters like what size the image is or how big it's going to be printed, QI, once configured, will automatically take into account your printer's resolution and medium and applies the scaling and sharpening it determines necessary, within the threshold you have setup beforehand.
Finally, the reason it has a raw converter is bacause QI was around before even Lightroom existed, and photographers who needed a fast turn-around could simply load their raws in, quickly apply some global adjustments and start making prints; it's still faster than LR today because it doesn't require a catalog. This is useful if you're, say, a sports photographer who has an assistant with a laptop and portable printer on the ready to make prints of the game as you're shooting.
Qimage is pretty deep to get into, but 90% of the parameters are set-and-forget types that you only configure once for your hardware and print preferences, after that it's all about setting paper size, type, and the layout of images on each sheet.
Edit: Also, DDI has pretty much had free updates/support for QI for a long long time, but Ultimate is too different to be considered a direct upgrade to the previous versions. Adobe screws people out of their money on a regular basis and no one complains.