i think one of the reasons they used a different design is that they wanted something different, the single pivot design has always worked for them but it must be hard to convince people to buy a new bike each year when the frame looks almost the same as the previous model it is replacing.
also as a 4 inch bike if they did the standard single pivot design they would have ended up making something similar to the sub 3 which they dropped a few years ago due to lack of sales.
this bike on the other hand has a more trail bike feel as opposed to an xc bike, even the standard st4 has relatively slack geometry.
but as far as the design of the suspension goes, i won't really argue with an engineer because i am not one! so i'll probably lose!!
but this design gives a really active ride while still being able to climb without any issues so that makes it a good design in my book. when i have been to various orange trade shows over the years they have always had proto linkage bikes on display to show the dealers that they are always looking at other options, this was the first linkage bike they were happy to produce the second was the blood, which also has a trail bike version in prototype stage, and now they are adding linkages to the new 225 and possibly the new patriot (or whatever they are going to call it) so they must feel it is time to go in another direction, or atleast give another option.
oh and the colour, it's not mint green, it's so bright that it won't take a good picture!!!
it is actually "neon green" according to orange's colour charts.