So when is this case being heard? Because it does not appear on any docket list I have been able to find for the supreme court... Further while I agree that U.S. v. Morrision shows that congress can not regulate non-econmoic activity... Macro use is definitely going to be more hotly contested as an economic activity then the violation of the violence against women act in that case (although this act is important and does offer a civil remedy to those who are victims).
Under U.S. v. Lopez Congress has plenary (absolute) power to regulate
1) Channels of Interstate Commerce - this includes highways waterways and more recently the internet...
2) Instrumentalities of Interstate Commerce - which includes people (in the course of business normally) trucks planes phones and the internet
3) Substantial Effects on Interstate Commerce - things that are done either by an individual or by a group instate
Now because macro use to "gold farm" is something done extensively in MMORPGS, and has in itself essentially become a virtual economy it is quite possible that congress may have power over the economic activities done while macroing.
Now this is all based on my understanding of the rule and since I am not a lawyer may be incorrect.
Still if you are going to argue aggregation know that in Gonzales v. Raich the supreme court ruled that intrastate growing of !@#$%^-*! use and growing under the compassionate use act was ruled to be an economic activity that could be regulated by congress. (they stated there was a national market for MJ, and that the effect of allowing it to be grown in California was going to have an aggregate effect on the price of MJ interstate even though the conduct was purely intrastate)
Based on that logic it could be interpreted that because "gold farming" and power leveling have a national market, and macro use makes for a difference in the price of these services then although the macro use could be limited to one state or even country it could in fact fall under congresses's commerce clause power.
granted I have seen no such case anywhere so I think we need not worry... but again im not a lawyer so I could be wrong.
The activity being regulated here is playing online games. I would imagine that if D3 required a monthly fee, then a restriction on macro usage would be a completely valid regulation since you're actively engaged in ISC when playing.
But, since D3 requires no online fee, you may not really be in interstate commerce after you purchase and play. So, you'd probably have to go with the substantial effects test, and I just can't see how internet game playing would be considered to have a substantial effect after the holding in Lopez. The Court would scrutinize the !@#$ out of that finding and probably conclude that it required too many inferences to get from Zerging Mephisto to a substantial effect on ISC and reject the law as an invalid exercise of CC power.