Fido also has the highest up front prices for any Top Tier phone in Canada on Contract other than the Razr HD.
Perhaps you should qualify that. eg. The BB10 is $350 up front on Fido, but it's for a 2-year contract. With Rogers it's only $140, but it requires a 3-year contract, and that 3-year contract usually costs more per month as well. However, if you really want to get it on a 3-year contract at Fido, you can also pay more per month and pay $150 up front, so I guess yeah, it's more expensive.

The big differentiator here though is the ability to buy it on a 2-year contract at Fido, which is a big savings overall.
BTW, two identical plans are $56 for the 2-year plan, and $67 for the 3-year plan, $11 per month more. However, those plans expired a few weeks back I believe. Current in-market plans are $60 for the 2-year plan, and $80 for the 3-year plan.
So why would anyone get a 3-year plan? Because phones like the iPhone are only available on 3-year plans (or else pre-paid). I personally won't be getting a 3-year contract any time soon.
I must be missing something, why on earth would you buy a Nexus 4 from a carrier?
Some of the carriers have extra incentives. eg. My wife has 3-digit $ in incentive Fido Dollars that can be used toward a new phone. It's currently $1xx sitting unused.
Secondly, if you buy it on contract, the price will be lower. My wife currently has no contract at all, and she is on a plan which is only $35 a month for 200 minutes plus unlimited evenings and weekends, no Canadian long distance or roaming charges (meaning all of Canada is considered a local call), unlimited SMS/MMS, voicemail, caller ID, and 250 MB data. That $35 plan is eligible for all phones on the carrier that have 2-year contracts.
Say Fido were to sell the Nexus 4 for $499.99 up front, but $199.99 on a 2-year contract plus $25 activation fee. That's $225 total on a 2-year contract. She doesn't want the phone, but if she did, she could sign a 2-year contract, and then apply her say $150 incentive dollars, and get the phone for $75. That's still a heluvalot cheaper than Google Play for that 16 GB model. She'd basically be getting the phone for $284 (plus tax) off, which amortized over 2-years is $11.83 per month... on a $35 plan, effectively making her plan about $23 a month.
And no, she can't get a better plan for much cheaper anywhere else, except on some of the really low end small carriers which have lousy coverage.