Have you been short changed? Well, yes, and no...
The 'basic' wheels on the Cross are 'off road' wheels, that are unique to the Cross and come with all season Goodyear Vector tyres, 185/65 R15 size.
You have spec'd the £300 option to fit '15" smoked alloys' - which are what the 4x4 and Trekking come with anyway. Adding this option also brings you smaller tyres (175/65 r15). In passing. this also reduces your offroad ground clearance by 6mm (to be the same as the 4x4 -- the 'extra' 6mm the Cross is quoted as having is entirely due to its standard tyres being slightly taller than those on the 4x4). So, your 'extra cost' option arguably delivers less than the standard wheels would have done
However, those wheels should have come with "Continental CrossContact Winter" tyres on them. Proper, winter tyres, not 'all seasons'., which should be better in snow. So yes, you should question the 'Eco' tyres. [later edit - see below...]
Here's the options as shown on Fiat configurator, which clearly states that the extra cost wheels come with smaller tyres, but does say 'M+S' tyres... and the tyres should look like this:
http://www.tyrereviews.co.uk/images/tyres/Continental-ContiCrossContact-Winter.jpg
[later..] But look at what happens if you select that option! The Configurator then throws up a box saying those wheels have to be fitted with 'Alternative Summer Tyres' at no extra cost! Why would they do that?! £300 option to fit the 'standard' 4x4 wheels and wrong tyres, making the car much less capable. Very odd (screenshot of this in second post as can't add here)