And since their price is 19.99, that's 500 million dollars - half a billion!
Not really. While I'm not denying that 25 million copies is impressive, Nowhere near that number will have been sold at $19.99.
For instance, there are various mobile versions which are counted as part of the Bejeweled franchise, that go for a few dollars a time. They also might be including deals to put demo versions on mobile handsets as part of their 'units sold' figure to dress it up a bit.
Should never take sales figures at face value.