While true, if it is written into the contract that they can add data to your plan if you have a phone that requires it, and you sign the contract, then they can add it.
Rogers' current version of the Wireless Services Guide (the glossy package that accompanies every SIM card they distribute) seems to contradict you.
link:
http://www.rogers.com/cms/pdf/en/ROG_1279_SEPT_UGD_EN_LRez.pdf
(See page 18).
It appears to say that the choice of premium monthly data subscriptions varies depending on whether or not you have a smartphone or a normal POS phone, but that either way, the baseline option is something called a "Day Pass" (which supersedes and replaces the previous per-KB pay-per-use rate), whereby you pay for data by the day (IIRC $2.99 per 20MB per day for smartphones, with each individual $2.99 charge requiring your explicit consent, and no data available at all until you give your consent), and you only pay for those days in which you actually use data.
It could very well be that they may require you to subscribe to a premium-priced data plan for a fixed term as a mandatory condition of receiving an equipment subsidy. And in order to opt out of such a data plan, a "Data Early Cancellation Fee" (DECF) would certainly apply, because the premium-priced data plans do come with their own sets of minimum terms, independent of the minimum term attached to the remainder of your wireless services.
And it may also very well be the case that certain (or even most) stores will have a policy to refuse to sell you a piece of equipment at all unless you agree to buy it at the subsidized price, with all the extra obligations that places on you, and along with all bonuses and commissions that the store will receive.