Having been a professional service engineer for over 45 years I'm also 'less than happy' about the three resistors in parallel, but on the basis of poor reliability. I've seen such design choices MANY times (either series or parallel) in commercial equipment, and it's one of the most common cause of faults that are 'designed in' from the beginning.
The reasons for doing it are obvious, as you've already explained (to some extent) - but the real reason is cost - it's cheaper for a manufacturer to fit multiple small resistors rather than one large one. However, this makes for an unreliable design, and a single larger wattage resistor would be far more reliable. There's also the added bonus that higher wattage resistors are rated for a higher voltage than smaller ones.
As an engineer, it makes many repairs simple to find - one of the first things to look for are series or parallel resistors in 'at risk' areas, and check those. I've even pointed out the design flaw on manufacturers courses, and pretty well always a couple of years down the line they will start to fail.
I've never been able to find out if this type of poor design choice comes from the actual designer, or the bean counters on the production line - I've certainly seen a few 'cost saving' measures implemented, where it was obviously not designed that way.
