TDP numbers from both AMD and intel are based on cpu running at full clock (amd also publishes numbers when running in lower p-states, not sure about intel). So no, there's no way it should draw 57W when it has a TDP of 35W. Now, in theory, you're right, TDP does not have to be the absolute maximum a cpu can output. However, all measurements I've seen indicate it's pretty much impossible to exceed TDP with any workload (IIRC, not even with Core2MaxPerf, a tool specifically designed to cause maximum power consumption).
Even if you somehow would exceed cooling system capability, you wouldn't need to downclock a lot. Since these cpus drop voltage when downclocking, going from 2.5Ghz to 2Ghz already drops power requirements by half or so (that's just a guesstimate but you get the idea).
That said, after reading some of the links, it seems it is some problem with cooling the chipset, plus some overly aggressive bios with way too low thermal thresholds for throttling. Dunno if that's a simple bios bug or there is some reason they do it (could for instance have some components where you don't know temperature but dell knows they get too hot). In any case, this is indeed clearly broken, and IMHO a obvious case for getting a replacement part (or refund if dell can't fix it). If dell isn't going to do something about it, probably some lawyers are going to have a lot of fun with this...