re your original question - sorry cannot imagine how many - or what proportion of pilots are rated.
But - it is the way the business is going. That is Corporate and Charter, Public Transport helicopter operations are, in my opinion, tending towards the twin engine, IFR capable aircraft. And instrument rated pilots are needed to fly them.
I think the industry, in UK (no experience elsewhere), is maturing, growing up (god forbid) and approaching 'stiff wing' standards of operation. Low level, marginal VFR, 'scud running' is no longer an acceptable operation. But, be careful not to assume that IFR necessarily equals 'bad weather'. The average B747 spends the vast majority of its flight in blue skies, but rarely, if ever, flies VFR. Rather, consider IFR flight as a higher level of safety for the fare paying passenger. This is most definitely not to detract from any VFR operation, my point, as above, is regarding Public Transport Ops only. Obviously a good portion of the helicopter world is involved in many other types of operation - where IFR would be irrelevant.
The same discussion can be had regarding helicopter performance. The new generation of machines just coming to market are able to demonstrate Class I performance at weights and in conditions that we have only dreamed of previously. This offers a whole new level of safety to the punter.
The point regarding airfield to airfield operations and their irrelevance to helicpter ops. is taken. But this is an important area that needs to be, and is being, addressed to further these developments.