I think they have a point here. For example, the PS3 has a load of services which are in the cloud, such as film rental and downloads as well as game downloads. A HD film or some games seem to be around 7GB to download, but my ISP caps at 20GB per month with £5 for an extra 5GB over that limit (£1 per GB, grrr!!). So basically these PS3 services have to be used with care, otherwise the cost of renting a film is suddenly a lot more than you pay at the Playstation Store.
The really stupid thing is that the ISP doesn't count usage between midnight and 8am, but the PS3 can't be set to schedule downloads in these 'off hours' unless you subscribe to Playstation Plus for an extra £40 a year.
As a result I don't use the Playstation Store for much, and well, haven't used it at all since they lost all the credit card details anyway!