Blow up a Mercury Racing package (525 through 1200) and see how many MerCruiser shops have a spare 600 supercharger, NXT input shaft or #6 gear set lying around, or the tools to fix them. The same holds true for Sterlings, Cobras, Potters, Teagues, Innovations, et al. All good products, but not run-of-the-mill. In the high-performance market, unless you are close to a specialty shop, you're depending on FedEx for parts and probably service. IlmorDude's right - Ilmor has been very careful to sneak into the market at a controlled pace and not get ahead of themselves. The engines are a relatively proven commodity, with Chrysler's engineering and Ilmor's careful development behind them. Note that Ilmor has yet to put a supercharger on anything; they're not sticking their neck out too far. Now that they have a drive designed to handle 1000 ft-lb/1000 hp, they are still limiting themselves to 725 hp, not going crazy right away.
In a way, the economic downturn has played right into their hands. While they may only get a couple dozen Indy drives out in 2009, that will be enough for them to see how they behave in the real world and if there are any inherent design or manufacturing issues that can be corrected before ramping up production to bigger numbers. It's the perfect beta-test scenario. Plus - Once the first batch has been out for a season or so, the rest of the potential buyers will have a higher level of confidence in going the Ilmor route for power once the market starts to come back.