It is a subsidy, they are subsidising £349 of the iPad for you (In the case of the £200 one), in return they request you guarantee them 24 months of business at £25 a month to obtain that subsidy, it is not unusual to put strings on a subsidy of any description.
You're getting confused between a credit agreement and the Total Cost of Ownership argument, and the TCO of a 3 iPad plan vs 3 iPad looks like this:
Subsidised iPad + data plan = £199 + (25 x 24) = £799
Full price iPad + data plan = £549 + ((15/10) * 15) * 24 = £1089 (the crazy price plan is calc is to up the 10gb to 15gb based on price per meg)
Even if you went on the rolling contract for the full 24 months
Full price iPad + data plan (£10 a month) = £909
On the cheap data plan
Full price iPad + data plan (£7.50 a month) = £729, but you only get a gig
If you're planning to get an iPad and use a 3G data connection this is a deal, cause it is a heck of a lot cheaper than the equivilant sim only deal, so yes, a subsidy. (even Orange's deal isn't awful, no where near as good as this one though)
Yes if you're dumb enough to go "£199 cool, then only £25 for 24 months and I'm never going to use the data plan", you're an idiot and you may as well burn your money in a pit to keep warm, if you're planning to use the data the deal is perfectly good and works out pretty cheap for the overall package, very cheap infact.