Hm, another thought: The russians had this pocket pistol (PSM) in 5,45 x 18mm able to defeat light body armor. Taking a closer look, that ammunition does deliver more or less the same power as a HV 22lr. does out of a pistol barrel, which argues against the statement that the .22lr is anyway to weak to penetrate much and hence doesn't need a FMJ...
5,45 x 18: 94 ft/lbf ME, max pressure: 25.000 PSI
22lr: ca. 90 ft/Ibf, max pressure: 24.000 PSI
not that much difference, but of course the 5,45 would be useless in terms of AP if utilizing just a lump of lead instead of a FMJ (and even hardcore) bullet...
http://en.wikipedia.org/wiki/5.45%C3%9718mm