Miki 2 was less of a resource hog than Vicki 3 or 4, she had fewer facail morphs to manage but you could command a huge variety of expressions. Her toes were jointed and could conform to shoes much better, and allowed much more precision in posing and were more realistic than V3 and V4's, but like V3 and V4 you could additionally pose them as a whole as well to save time. She has options V3 and V4 don't have and it also breaks up the monotony of using V3 and V4 over and over in scenes. Miki2 had a neck seam issue that was corrected for D|S by a group of talented users over at the Daz forums, and some additional 3rd party options for her expanded the functionality of Studio because of the user base who was interested in using her (like the ability to inject a PMD file)

But yea, I'm sure its going to annoy the Poser 7 users more who are using software that's only 4 years old when they're told, it's not going to work, you need to upgrade to a questionably less stable piece of software that's going to cost you between $150 and $250 to do so.