The goal is clear: make icons look pixel-perfect under any supported resolution which is a tought task indeed, especially taking into account that Inkscape is not the best tool for this kind of work. But just look at the results! The technique level is approaching the one of Mezich, one of my favorite icon designers (mostly because of his pixel-perfect icons) and is definitely better than downsampled bitmap icons used in Tango before.
For the time of its existance Tango desktop suite has passed a way from a set of blurry pictograms to a serious guidelines, resulting a series of interesting icon suites. Just to mention default Tango set and famous Tangerine (Ubuntu) icon set, created by the same team that worked on default Windows XP icons.
So far Tango and its derivatives seem to be the only good set of icons, available to both commercial and opensource software developers for free and its quality is good enough even to compete with some commercial icon sets.