Gosh, why wouldn't you? I have 6 currently. One for each member of the 4-person family (two small children). A spare. And a senior's card for when the grandparents are around. The spare get's used often enough ... it's only the Senior's one that sees not much usage.
But the article is about accounts, not cards. I'm not sure why one would want separate accounts, for the same email address. But if you really do - gosh, just create another gmail address - what's the big deal?
Oh, that has interesting implications.
Another reason to need two cards currently, is to use the downtown express. Either you pay 2 cash fares, 2 tokens, or use 2 different Presto cards to pay - or some combination.
GO is 3 hours. Sometimes I've simply forgotten something at work - I kick myself, but usually wait until midnight or so, and just drive in quickly. A soccer game is normally 90 minutes plus a 15-minute break and injury time. If I go straight to the game and back again, I have no problem paying nothing to ride GO home, and see the opening and closing whistles. Rugby League games (which are at Lamport, right beside Exhibition GO) are only 80 minutes long plus a 10-minute break at the half, and some injury time.