Because on SB and BB you are getting better pot odds
. Assuming people call before you, you sometimes get 9-to-1 or 10-to-1 odds. It defenitely makes it worth to defend with suited connectors, or sometimes even hands like 9To or AXo or (and this is my preference) J9s.
I actually don't know what PokerStrategy says abour your range at BB, but it should be around the same, maybe even bigger, for the same reason: it costs way less for you to call. If BB is $20 and someone raised to $40, everyone else is getting around 2-to-1 (20+10+40 - to - 40) for entering the pot, while you get 4-to-1. Doubles your advantage over them and thus your range. And in the BB there's still the chance everyone checks to you and you enter for free.