I'm not sure that they could have made DoTs tick down faster without a ton more code rewrite than they wanted to do. DoTs are basically buffs that tell the game to deduct the HP, and the game checks it every 3 seconds. That mechanic is why you do not really know exactly when within that 3 second window the HP gets deducted (especially if in combat with a party or a raid). Its not like other MMO's where the DoT is doing the damage and you get a report based on each DoT. It would have required a rewrite of the entire DoT system, going from a universal system to a DoT-specific system, for DoTs to tick down faster.
That said, if DoTs DID tick down faster, one of two things would have been the result : either the timer counted down faster as well, requiring more frequent DoT casts, OR the time between damage applications would have been reduced without affecting the timer, creating a potentially huge granularity in terms of how effective each point of SpS is. What I mean by that is, on a 18 second DoT, if you go from 3.0 second ticks to 2.9 second ticks, how many more ticks (damage applications) do you actually get? One? None? Assuming that the DoT will NOT do damage at 0 seconds remaining, on a 18 second DoT :
3.0 second ticks : Initial, 3.0, 6.0, 9.0, 12.0, 15.0
2.9 second ticks : Initial, 2.9, 5.8, 8.7, 11.6, 14.5, 17.4 (+1)
2.8 second ticks : Initial, 2.8, 5.6, 8.4, 11.2, 14.0, 16.8 (+0)
2.7 second ticks : Initial, 2.7, 5.4, 8.1, 10.8, 13.5, 16.2 (+0)
2.6 second ticks : Initial, 2.6, 5.2, 7.8, 10.4, 13.0, 15.6 (+0)
2.5 second ticks : Initial, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5 (+1)
2.4 second ticks : Initial, 2.4, 4.8, 7.2, 09.6, 12.0, 14.4, 16.8 (+0)
2.3 second ticks : Initial, 2.3, 4.6, 6.9, 09.2, 11.5, 13.8, 16.1 (+0)
2.2 second ticks : Initial, 2.2, 4.4, 6.6, 08.8, 11.0, 13.2, 15.4, 17.6 (+1)
2.1 second ticks : Initial, 2.1, 4.2, 6.3, 08.4, 10.5, 12.6, 14.7, 16.8 (+0)
2.0 second ticks : Initial, 2.0, 4.0, 6.0, 08.8, 10.0, 12.0, 14.0, 16.0 (+0)
As you can see from this, you have to greduce the time between damage applications quite a bit in order to derive any benefit from it at all. I know people would assume that you would go by your hasted GCD timer, but that assumption is only that, an assumption, and they could have put in whatever scale they wanted to. Indeed, they would have had to continually do a scale value reset, as gear levels rise and SpS amounts rise, though that is also an issue with nukes and not just DoTs. Going from a 3.0 second tick time (6 damage applications) to 2.9 gives you one more damage application (7 of them) but it then takes getting down to a 2.5 second timer before you get another damage application. Things do speed up the lower you can get the tick interval, but (making that same assumption regarding SpS) it is unlikely that we can achieve levels of SpS sufficient to provide more than a couple of damage ticks.
Having SpS act in a manner similar to Det on DoTs makes more sense, once you think about it.
