"In the US, it's perfectly legal to fly a single-engine helicopter at night, across cities, with no IFR instrumentation at all"
Then the FAA get all shirty when BA decide to fly a 4 engine aircraft on 3, back home; there's consistency!
Going back to the original debate about twins, is it really going to cause any problem for the pilot to operate a 427 rather than a 407/206, or a 355 rather than a 350/120? We've operated 355s on high intensity operations without any problems (they took over from a 206).
The defence of lack of VSIs because it's not a legal requirement is novel. Lots of things may not be legal requirements, but it doesn't mean they are probably more than desirable. I imagine in 'gold fish bowl' conditions it would be highly desirable to have all the instruments you can, even if technically VFR. By not fitting such gear seems to imply that the owners are aiming at the lowest standard they can get away with, rather than the highest standard practical (there obviously comes a point where kit for the sake of kit is not helping anyone.) It seems less than diligent on the part of the FAA too; it (insert particular item) may not be a requirement now, but perhaps it ought to be.
Take AVADs in larger a/c such as the S-76 for example. In the UK in 1986 (I think) an S-61 full of passengers flew into flat calm sea in the cruise whilst VFR, but in heavy haze, resulting in several fatalities. Subsequently the CAA mandated AVAD for aircraft operating over water. A relatively simple, cheap and effective way to prevent a repeat performance. Indeed, it probably saved a 76 a year or so later. Has anything been mandated following the CFIT last year of a 76 at night in the GoM? So not all our regulations are 'anal' and not everything is tied up in how many engines we have; most rules are a result of experience and reacting to events that have taken place. In some cases, even proactively such as HOMP.
Having said that, I think it is also important to realise that unlike some 'oil patches' in the world where there may only be one, two or three operators, in the GoM there are loads of them, several of which most people outside the region won't have heard of, and it is wrong to tar all of them with the same brush.