Nothing unusual and also applicable for other manufacturers and petrol cars. You loose warranty of course, but some people still opt for "chip" tuning right after buying. Others might wait the 4 years.
It's not uncommon to find models with a wide range of power outputs but the exact same mechanical parts, and the only difference is the program in the ECU. Before electronics, the difference might be in a few small parts[1]. If you spend long enough staring at parts catalogs you can easily spot such things.
[1] One of the examples that immediately comes to mind is with diesel engines --- you can change the fuel injectors to tune power over a very wide range, limited only by your acceptance of fuel consumption and emissions. All the load-bearing parts of the engine (block, rotating assembly, etc.) are exactly the same: http://forums.aths.org/Attachment20581.aspx
I recently replaced my starter motor ('09 though, so I definitely don't have the feature,) so I'd be wary of that, but don't they fit longer-durability starter motors in those cars?
Actually, come to think of it, (please correct me if I'm wrong) they probably keep the fuel pump primed while 'on' but at a stop, but I'd be concerned about the lack of oil at engine start. I always was told to turn the key to on, wait for the ~2 seconds for the fuel pump to prime and after you start the engine, and let it run a bit before starting to drive.
My cynical side wants to think the start/stop is a planned obsolescence 'feature,' but obviously I don't really know for sure.
It's an attempt at squeezing the tiny last bit of fuel mileage out in the standardised tests, and they obviously don't care if it wears things out faster...
In theory, Apple could detect this (previously jailbroken state) when they plug in your device at the store to do diagnostics, but (at least 5 years ago) I’ve brought a few “restored from backup” devices in for service and they don’t say anything. I guess as long as it isn’t currently jailbroken, they don’t care.[c]
[a]: /Applications contains apps that come with the device and can’t be removed (such as Settings, etc.); Cydia installs itself and any apps you install through it into this folder. OTOH, apps installed through the App Store go under /var/mobile/Containers.
[b]: The reason being: pre-jailbreak, / is mounted read-only, but /var/mobile is read-write. So iOS works on the assumption that any app installed to /Applications can’t keep its config files with it, so they’re put in /var/mobile/Library.
[c]: Simply hiding the icons of Cydia and apps wouldn’t be enough to convince them as jailbreaking involves disabling a few daemons (the biggest is the OTA update checker; they don’t work well with a jailbroken device), so Apple’s diagnostics would probably show that some daemons aren’t running (that normally would be).