Other than California, the requirement only applies to new trucks. The $9k cost is BS. The SCR catalyst has no precious metal on it so probably only adds $250 or so. The injection system, tank and pump typically has a target price of less than $1500.
When people talk of a cost of $8k, they may be talking about the entire aftertreatment system, so downpipe, Oxidation catalyst, soot filter, SCR system, Injection system, pump, tank, heat shields, hangers, muffler, stack, stanctions etc. And that would not be the OE cost, it may be replacement cost with their big mark up added.
The new vehicles that will be sold in 2010 and 2011 are just a drop in the ocean when compared to the entire transport fleet that already exists. Eventually (in 2 decades) the legislation will have a noticible effect on air quality, but it is going to take some time to get there, until all the old trucks are worn out.
Typical strategy for the urea on passenger vehicles is that the urea tank is sized to cover the mileage between service intervals and the dealer refils it when doing the service. Commercial vehicles will have a urea pump next to the diesel pump so they can fill both at the same time. Only a small % of urea is consumed per gal of diesel, since it is a catalyst. If the type of vehicle service dictates high power and thus high fuel consumption, more urea will be consumed requiring more frequent topping up of the tank.
There are really 3 different strategies available for reducing nitrogen oxide emissions
The oldest is using a nox adsorber which "stores" the nox for short periods and then periodically "regenerated" by running rich. The Nox adsorber needs a lot of precious metal, a limited number of 2007 onward Dodge rams had them and the NOX adsorber was rumored to cost over $1000 alone. Hence the spate of incidents where gangs or "inside jobs" saw off all the exhaust systems from the trucks at night and the owners face a very expensive repair the next day.
The next is the Urea selective catalytic reduction system. Urea is vaporized in the exhaust, where it dissociates into amonia. The amonia and the nitrous oxides react in a catalyst comprised of base metals (cheap) to produce nitrogen. Gasseous amonia would be great for system designers, except for the fact that it is deadly. Urea is a relatively benign way to package amonia, except it is terrible stuff to work with at the system level. Keeps lots of people employed as a result. Urea SCR was launched in Europe in 2003 by Mercedes, so the european have several years experience with it.
A more recent system is hydrocarbon selective catalytic reduction, where typically a reformer is used to burn fuel and produce a gaseous cocktail which will react with nox in a catalyst which may or may not contain precious metal. This is the technology the japanese OE's are developing.
Several factors influence the choice an OE will make regarding which strategy to follow. For 7L+ truck engines, any system based on a platinum catalyst is very expensive in first cost. On top of that, even with the sulphur reductions that have been made, there is still sufficient in the fuel to degrade the performance of the catalyst over time. So to compensate, OE's either have to increase the precious metal loading (mega $) or face a situation where the catalyst may have to be considered a service item (replace after XXXXX miles). Needing to replace very expensive catalysts as a service item does not sit well with most fleet owners (same with soot filters) so in the interest of customer satisfaction these systems typically need to be engineered to never be serviced within the waranty period. That can be over 1 million miles expected service life on large commercial vehicles.
By comparison, the urea SCR systems do not have the same up front cost, but they do have to be engineered for the application, with the heated lines and tank and lots of work calibrating the engine management.
Not enough is known about the hydrocarbon SCR systems yet to consider them low risk. Whether the fuel reformers will go the distance or pose a huge service problem etc has been a sufficient deterrent for most OE's to bypass them for now. I was under the impression that International is fighting the EPA in court regarding the emissions requirement, so right now the only thing that is clear is that if they lose they will probably have no sales next year, since they have not developed a system.
This requirement for 2010 SCR reduction systems was one reason CAT got out of the on road truck engine business. International was meant to have taken over this role, but now it is really not clear what will happen. Considering that every other OE has a system ready to go, I would be amazed if the courts found in International's favor.