The change you're talking about was the second, the first one here: https://github.com/evan82/darkcoin/commit/ab58f240aca5b43e22b990c4a872fce4174bcf80

Right now it's already 4th version.

The latest changes (https://github.com/evan82/darkcoin/commit/970f9d202aeb90c5d9168736a07c05ed0e2fc448) was made as to prevent a possible attack https://bitcointalk.org/index.php?topic=421615.msg5348513#msg5348513. But it could be prevented by starting more p2pools, and I see the change as an attempt to limit reward to 25, so if the coin lose popularity nobody could get blocks with up to 153 coins.