You must understand what beta used to really mean - it was supposed to be BETA test, that means that you add features into the game, and somebody has to test those features as we are doing right now.
What EA and other guys do is usually much closer to final performance/stress testing, when they usually test how their infrastructure holds up during their free weekend session - if their servers survive those insane influxes of players (6,4 mil for division in 3 days? huuuuge) they know their servers can handle anything Squishing some final absolutely minor bugs on already thoroughly tested game is just minor bonus.