Usually they do Greg, this time however, and this is my personal opinion, we have California to thank.
CARB has been waging a war on the smog part of pollution (NOx) as it is a particularly bad problem in Cali due to some geographical factors. CARB was going ahead with it's own super strict regulations and I think the EPA woke up and decided that they better get their rules more in line with CARB's or it would result in an economic island so to speak and severely disrupt interstate trade. So they decided to play catch up.
Particulate matter is (my opinion) more of a health and air quality concern but the optics of brown haze over LA and the political sexiness of being able to say "we are doing something dear voter!" has I believe got us to this point.
The PM limits for EPA2010 are .01 g/hp/hr and Euro5 it is .02g/kw/h. There is .746 of a kw in a hp. In that respect the Euro limit is around .014 g/hp/hr. Euro 6 (2013) is going to be .007 g/hp/hr. So EPA 2010 is in between the two.
When it comes to NOx, EPA 2010 is .02 g/hp/hr, Euro 5 is 1.492 g/hp/hr. As you can see that is quite a bit (realatively speaking) higher than EPA. This would lend itself to the EGR free Euro 5 engine Moose is talking about (EGR is a NOx fighter, nothing else). Of note, Euro 6 is still going to be .373 g/hp/hr.
Fighting NOx is the difficult thing to do, it brought us to EGR, EGR makes the combustion very dirty, resulting in the need for DPF (soot filters). We had super clean diesels in 1994-98 except for NOx. When someone finally perfects a practical NOx absorber (Eaton for one is working hard on this) happy days will indeed be here again and we will get back all of our fuel economy. The reason I like SCR so much is it gets us part of the way there, by letting the engine burn efficient again and cleaning up the exhaust after the fact.
If I keep writing answers like this people are going to start calling me Turtle II.