I cannot see the logic that M3 resupply makes the hordes bigger.
At City 100% and a working GV spawn to the town, it does (Town downtime 30mins, -10mins per single supply drop). If M3s are able running, you only have a
very short time frame to capture and it takes much more effort in short time.
Addendum:
Let me add that the overall net effect on the rate base capture has still been negligible. While it is more difficult to capture towns at City=100% under the 'new' strat system introduced in 2012, it has also become easier whent he City has been hit considerably.
Both effects seem to even things out overall, as the rate of base captures has not changed significantly compared to pre- August 2012.
The one thing that did have a tremendous impact was the introduction of the new towns itself.