Well there was some degree of merging already back in rigger2/3 where they had a emulator module that allowed deckers to connect to security rigger setups.
So from a rules standpoint it is understandable that one want to fold those into each other as there was more and more of a overlap of capability of not specific rules. Especially once the matrix became wireless as the norm rather then exception.
I think the merger was inevitable but I still don't like it. The Rigger and Decker had two very distinct feeling about them (which is why you see a lot of RIgger Hackers now). The Rigger was the master of the droid army, the Decker was the master of the matrix.
And to some degree that is still the case, as while there is a overlap in skills and programs there is still the cost issue (tho the hacker quickly runs out of goodies to spend nuyen on, unless he starts to dabble in micro-drones for those pesky ultra-secure hardlinks only setups).
