Some of you may need to look again at the definition of a metro area... or rather a MSA (Metropolitan Statistical Area, or Micropolitan Statistical Area) as used in reaching these numbers.
The general concept of a metropolitan or micropolitan statistical area is that of a core area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that core.
Annexing land may or may not have anything to do with a MSA. A good rule of thumb is to look at where people commute to work. If it's a majority, they are a MSA. This explains Riverside/Ontario being separate from Orange County and Los Angeles, for example.
AAJAX, apparently they did annex some type of land.
Perhaps this raised the actual city of St. Louis' population. However, I believe well over 100 municipalities make up the St. Louis MSA, including about 80 in St. Louis county alone, plus unincorporated areas (where I live in Wildwood was unincorporated until relatively recently).
MSAs and airport catchment areas do not necessarily add up. Jacksonville's airport serves more than just Jacksonville, but as far away as Brunswick, Gainesville, and Valdosta. Omaha's airport serves much more than just Omaha's MSA, as people drive from as far as three hours away to use the airport (including many from Des Moines, which has its own airport, due to the lower airfares). St. Louis has people driving from places like Marion, Cape Girardeau, and Columbia, which may have their own airline service but come to STL
for lower airfares on certain carriers. I'm sure there's a more accurate list of how many people each airport actually serves out there.