Tier 4 standards were introduced as part of the Clean Air Nonroad Diesel Rule signed by President Bush in 2004. This same rule required the removal of sulfur from diesel fuel by 2010. http://www.hobbyfarms.com/farm-industry-news/2010/03/18/emmission-standards-toughen-for-diesels.aspxThose standards appear to be what created Tier 2 emissions controls, mostly removing the sulfur from diesel. Tier 4 started shortly after 2009 and was fully in place by 2014 in agriculture. I don't think Bush was directly responsible for Tier 4 but some of his appointees may still have been on the committee responsible for establishing it.
Sad the manufacturers waited to the last minute to try someting. All the tractor companies have different systems. One will work the best. Like you said, we pay for it.