The biggest driver for fitting these iridium plugs is the mileage between changes - at a dealer, you're going to pay a lot more to fit three sets of steel plugs than it will cost to fit one set of iridium, simply because of the labour costs. The listed plug for this engine is the NGK DIFR6D13, and that's what the dealer would fit.
There is some logic in fitting iridium even if you DIY - it's a bit of a job to get the plugs on the VTEC, I'm not sure I would want to do that every 2 years unless I had to. If you don't mind the dismantling to get to the plugs, the steel tipped plugs are cheap, and it would be interesting to hear how many other VTEC owners are using the BKR6E-11.
As for longevity, 100,000Km or 72,000 miles does seem rather a lot, but not having had a VTEC long enough to change the plugs, I wouldn't know if it's a problem. On a Ford I had with the 2.3 engine, I know that the tips on the platinum plugs were almost burnt off by the time the 40,000 interval was up - you had to change them, or you would soon have problems.
