No, sadly it seems not to work like this. On 1 of my 2 accounts banned I had a Barb which I cleared Inferno with, and also was normally playing, not only botting. It was like 3-4 hours of normal play, 2 hours break, ~6 hours botting. And it was banned anyway (luckily i managed to get it back :3 ) Other two accounts were botting only and 21+h/7 for over 2-3 weeks. 1 was banned and 1 was spared.
It all looks too random to me. Either they're doing it by hand and sometimes they just simply miss some accounts, or they simply do it for purpose so we wouldn't know what's their key for bans.
About Accounts:
All are EU
1st banned (this one I got back):
Private AutoIT script running Sarkoth 5-6hours a day, 3-4 hours of normal farming (play thoroughs of Act 2 and 3 inferno), played since release
2nd banned:
1month old, at first for one week Private AHK script for endless ZK 12-16hpurs a day with 15-30min breaks (I was boosting ppl on HC for money), then 3 weeks of 21+/7 Sarkoth Private AutoIT script. Also progressed through Act 1 and 2 on Inferno in meantime (borrowed gear from friend).
3rd spared:
2 weeks old, just dinged 60 and from then on only Sarkoth 21+/7. Only one lvl 60 character on account, got boosted, missed most of quests for all difficulties, dinged 60, finished 1st quest and from then on it was straight botting. Yet for this most obvious from all 3 accounts, this is the only one that didn't get banned...