No...the quiescent current is comparable to other late model Jags. I think two issues conspire on the X150:
1. The electronics are particularly prone to malfunction during the voltage drop when starting the car, if the battery is not robust.

2. Many owners drive these cars only occasionally, leading to a lot of not very robust batteries.

 

Sorry, typo - it should be 30 mA (i.e. milliamps, not milliwatts). Of course, it's higher if you have a tracker fitted.

I think the issue is the very large current draw (at least 10A, probably more because that's the steady-state draw) that happens as soon as you open the door. The whole car wakes up all at once, and the large draw can result in a voltage drop if the battery is not sufficiently charged. If that happens, some of the modules either fail to boot or detect spurious error conditions which throw up error messages & fault lights.

(Edit: Sorry, Steve, I've basically repeated what you said; too slow posting)

But you're right, there's something weird about it all. I say that because of the variable nature of the problem. As far as I know, my car still has its original battery, so it's over 4 years old. It is not driven daily; maybe twice a week, and not for long runs. Yet I seldom have any problems - very occasionally the touchscreen has a sulk and won't get past the splash screen. Other people have newer cars and drive them every day and yet, if they leave them for a couple of days, the dash lights up like a Xmas tree.