So, Nissan can not undercut the price too much for the G25 otherwise it won't be profitable. This is a different scenario compared to lets say the TSX; the V6 version probably costs more to manufacture so a increase in price makes a bit more sense for the V6 version compared to the I4 TSX.
But it's very similar to what Lexus faces with the IS250/IS350. And Mercedes with the C300/C350. And BMW before the advent of the N54 engine, when it was 325i/330i. In all of these cases, it doesn't make sense to have the cheaper one far cheaper simply from a manufacturing perspective, but I think they made some standard equipment optional on the lower trims in order to have a reasonable price gap.
The situation is different in Canada:
BMW has the 323i Luxury Edition (2.5L I6 with 200HP) which is similarly priced as the base Infiniti G25.
MB has the C250/C250 4Matic (2.5L V6 with 200HP) which are also similarly priced as the base Infiniti G25/G25X.
And these 2 models are the major reasons why the 3 series and C-Class are at the top of this segment in Canada.
(Have a look at the chart from GoodCarBadCar)
Imagine how sales numbers would change in US if these 2 models were offered at at price point around US$32,000~$34,000 fully loaded (= base prices of 328 and C300)!