I understand why they are trying to keep the names consistent. It is for branding purposes. If you constantly change a name by adding a number or variation you lose the marketing consistency and value that having the same name for multiple generations of a device will create. They could have conceivably added an HD on the end but then what happens when they come out in a year or two with a 4k resolution Nexus 7? Call it Nexus 7 4k? It's best to just leave the name the same. That's why Apple did the same and keeps a consistent naming strategy for their devices. You see the same with car models. A Honda Accord is a Honda Accord regardless if it's from 1980 or 2013...tremendous brand equity builds when the same name is used for multiple generations and now that the Android device market is maturing we're going to see companies do this more and more.
You can see it with Samsung's Galaxy brand, the HTC One brand and soon the LG G brand etc.
On a related note....Nexus will most likely call the next Nexus phone the Nexus 4 again, unless the screen size is boosted to 5 inches or more in which case it's possible they could go with Nexus 5. If the screen remains what it is today I fully expect them to just leave the name Nexus 4, as it reflects the screen size.
Some people erroneously thought that the reason the Nexus 4 was called that was because it was the 4th generation phone. That was inaccurate. It was always about the screen size...just like the Nexus 10 is a 10+ inch screen and the Nexus 7 is a 7+inch screen.