Full power Norma 10mm Auto loads were never issue by the FBI. The FBI tests in 1989 were heavily weighted towards what would become 40 S&W ballistics, with only one of the 5 10mm loads tested making more than 1,000 fps. They tested 170 gr (Norma, 1358 fps avg), three 180 gr (Federal, Winchester and IMP-3D at 931 fps, 955 fps, 991 fps avg respectively) and 191 gr (Buffalo Bore, 916 fps). They adopted the Federal 180 grain JHP.
I have read, but not substantiated, that this loading was based on early, pre-test observations that the Colt Delta Elites were not handling the full power Norma loads well. Supposedly someone in the lab bought some 180 grain JHP's and loaded them to around 950 fps. They liked this load, and convinced Federal to provide some factory loads to this spec. Since so many of the tested loads mimic these ballistics, it is likely this spec pre-dated the test.
Given the momentum numbers for the power level of the load they adopted, the 45 acp springs were probably correct. This load generates very similar energy and momentum to the 45 ACP rounds included in the test. However, I have never heard of issue 1076's that were under sprung. The Delta's used in the test most likely were under-sprung. I know the Delta I bought in 92 was, and the one my college roomate had in 89 was as well.
Most notably, they 'solved' the excessive recoil problem by switching to a lighter gun (Glock 23 - 21 oz vs 1076 40 oz) firing the same projectile at the same speed (180 gr .400" JHP at 950 fps). This means they fixed the complaints about excessive recoil by using a new platform that would have more recoil than the old one.
Zoogster nailed it though about mfg. In the late '80's everyone was tooling up to make some variant of the 'wonder-nine'. The 10mm was going to require all new engineering and tooling. The 40 S&W though would drop right into about any wonder-nine frame with just a new barrel and breech face. If you owned a company, would you back the round that would cost you hundreds of thousands to tool to for, or the one you could be shipping guns in a month with only some changes to existing parts?
At the end of the day, the only two tested ammunition to score 100% in the FBI's 1989 tests were the 158 gr Federal .357 Mag at 1183 fps and the 170 gr Norma 10mm at 1358 fps.
The full power 10mm loads were largely rejected due to the recoil and concerns over gun longevity. Ultimately, neither were particularly valid in my mind. The S&W 1076 has proven itself more than capable over the years of the handling full power 10mm loads. And, the recoil of the 170 gr JHP at 1358 fps in a 40 oz gun is probably not significantly worse than the recoil of the current 180 gr JHP at 980 fps in a 20 oz gun.