There are no iFixit teardowns of Optimus G to compare all the chipsets side by side so i doubt this claim can be made as 100% correct, unless you can show me one where all the chips like UMTS amplifiers etc from BOTH are listed...
The thing is, the Nexus 4 was never meant to support LTE. It is clearly based on the Optimus G. The fact that the Nexus 4 has this tells you that the Nexus 4 wasn't just built from scratch bringing together similar components. They are likely using the exact same logic board with
all of the same components, including CPU, RAM, amplifiers, screen, and even the exact same battery.
If you are to go about building a smartphone that you know will be based on another phone, you have two options. You can either price out similar components and redesign the logic board and how it all fits together and go through various testing stages to get everything working properly. Or you can just use the exact same logic board with all the included chips and amplifiers and eliminate the costly testing and designing phase. Considering Google's desire to keep the cost as low as possible, this is clearly the more likely option.
Not to mention the fact that there are hacks to turn an Optimus G into a Nexus 4. And I'm not just talking about flashing a stock ROM.
Really, the LTE chip is the biggest piece of evidence. Why include it if you are just bringing together a bunch of components separately and redesigning the logic board?
You wouldn't. The only explanation for including it is because it is the same logic board that goes with the Optimus G. That is why all reviewers say they feel so similar. Speaker placement is the same, camera placement is the same, ear piece placement is the same. Everything besides the outter casing is the same.
There is so much evidence to show that they are built on the same components and that the only differences are on the outside. All you have to do is use a little logic and think it through. But if you insist that they are built with major internal differences, please show some evidence. Because logically and practically for all companies involved, what you are saying makes no sense.