Those things are a means to an end, the company doesn't exist to hold people's money. Banks do, since they loan out money at a fractional reserve. Coinbase makes money by btc going through them. Of course they have to hold bitcoin and of course it is more advantageous to hold some USD so people can trade instantly.
The original post was about them being like a bank, which is not true in the context of their business model.
> Those things are a means to an end, the company doesn't exist to hold people's money
Yet. Like the OP said, "Next up they'll probably offer interest and loans/mortgages". Who knows what else they'll divert their attentions to (hint: it's probably where the money is).
Coinbase seems to be going for the Payment Processor route, now with the USD wallet who knows if they'll offer you a CC just like Xapo. Guess who else offers you CCs?
The original post was about them being like a bank, which is not true in the context of their business model.