Hey Nuts..Anthon,
Just my two cents...from what I understand the 03 and 04 bergs were put together and rolled of the KTM line in Mattinghoffen, so I guess the adds are correct, my 04' 550 share's a ton of components with the EXC range, ignition, wiring loom, carb, tree's rims, discs, controls, switch blocks...but it's a Berg, not a KTM.
As for the start of the button, from dead cold even with the bike being hooked up to a C tek smart charger while sitting between rides, it will never start from stone cold off the button. It will start first or second kick nearly every time on the kicker. Given that, if the engine has even the smallest amount of heat in it it'll crank to life straight up....in the middle of an Aussie summer though, sometimes it'll start with the button from dead cold, but if you don't get it within 4 revolutions it's time to reach for the kicker
As far as reliability mine gets looked after well, oil and filters each 400K's....good Delo oil and a fresh air cleaner every time I get on it and it's been flawless over the years, I love the thing....Having come from a long line of brand new KTM's and Husky's this is the only pre loved bike I've owned in nearly 10 years and it's without doubt one of my favourite machines in the stable, I've thought about an upgrade to a new 501 but just can't part with the 550...it's just too much fun and not many people go past me, so for now I think it'll do just fine
Cheers