Actually Telstra (and the other companies receiving the 1c transactions) are probably the ones being hit hardest by this. Most credit card processing merchants will charge a percentage of the transaction value PLUS a small, static fee, which is usually about 30c. That means each card sending them transactions is probably costing them ~$450/month in fees. They just wouldn't notice it because it's in the noise, their bill from the merchant is probably hundreds of thousands.
Yes BW is probably buying the points, but I don't think it'd be more than $25/card/month (~0.3c/point). But still it's probably more easily noticeable for them that their points spend for these non-credit card accounts is so high (thanks to us).
Haven't got a letter yet myself, but a buddy who's only had his (1 card) going for 2 months now got one today.