Yes it would, the Iridium replacements aren't standard parts.
Of course, some folks doing the job themselves might keep the old ones to swap back before taking the car in for warranty work
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Sure.
One of the things which has moved on a long way in the past 50 years is metallurgy & materials technology - probably the prime reason why modern cars are so much more reliable and need much less servicing.
Iridium is a far, far harder metal than copper; the centre electrode on an iridium plug is much finer than on its copper cored equivalent and has much sharper edges; it also wears at perhaps a tenth of the rate.
Sparks discharge more reliably from sharp points; also the finer diameter electrode makes spark placement both more precise and more consistent.
Another factor is the move toward adding ethanol to fuel. This inevitably means the fuel will also contain some water (ethanol is hygroscopic); this makes the fuel more corrosive (particularly this is an issue if the engine is run briefly and stopped before it's fully warm). Ir plugs also have superior corrosion resistance.
Yes, they cost about twice the price of copper cored plugs, but they'll last at least four times as long; the savings in time (if you do your own servicing) or labour costs (if you take it to a garage) also help to make Ir plugs a more cost effective option in the longer term.
They say a picture paints a thousand words, so here's one I posted earlier (the OEM copper cored plug is the one at the top). This is one of those pictures where it really does pay to 'click to enlarge'.
