The thing about IS vs ES is that Lexus needs to sell two cars in segment to satisfy these differing tastes whereas the Germans sell both in one package, thats the reason you see the split. Plus it helps that the ES is based on Avalon/CAmry, plus its basically the car that put lexus on the map and simultaneously naild Caddy and Lincoln to the board, that caries a TON of weight especially with these older folks.
But we also have to consider that the buying population is far more vast then just your mum.
And the soccer mum crowd you're referencing, you've overlooked an important factor. These people want to be the same but a different same, see its not about actually being different but looking like you're actually being different. NX provides them with that difference without actually leaving the bubble. They still get a reputable luxury brand that all their friends will respect, but they also get to have something their friends don't have. Don't underestimate that type of petty pull.
That or they'll just buy MKC's
I agree with your first paragraph...and thus two cars in one price bracket and both selling well. With each, they appeal to different groups of people...thus, supporting what i said earlier. Folks who shop for ES won't look at IS and vice versa. And having two cars in the same/similar price bracket does NOT necessarily mean that one vehicle will eat the other sales.
If soccer moms want to be different, then they will look elsewhere...why do you think there are a ton of Lexus RX's at soccer games? Why do you think that there are a ton of Lexus ES at domino's night? No one is buying an RX to be "different" or "hip"...and as stats shown, there are a ton of folks who buy RX to be pretty much the same...folks who value practicality, reliability, durability, and luxury.
Moms who want to be different? They buy something else, like BMW X5, Escalades, etc..
The NX may bring some of these "different" moms back to Lexus...i agree 100%. But that was not my argument at all. The folks that NX brings back (due to difference factor) were never in the RX crowd to begin with.
So, again, having the NX in the lineup will do very little (if at all) to RX sales. That is my point.
I am not sure what you guys are disagreeing with me about...but i think that we share similar views...just expressed differently!