-
It's more the price difference for the good ones. The cost of chroming all that material to a high level means you can easily spend the best part of a grand for the cheaper brand ones. There's just not much on offer in the middle ground.
You're right though, it pays developers to spend money on taps and fittings which are likely to affect your perception of the quality of the build, the rest of it is often whatever they can get away with.
Disappointing what people will do to cut corners when they're working to a price on jobs.
You'd probably want to add some more depending on how much water you have to empty out of the system when you change the rad. I wouldn't assume that the job was done properly in the first place and the fittings might have just been cheap enough to suffer from this kind of failure. Would be typical for new builds to price things like towel rails down to the minimum.