Explain how the quality of them has deteriorated
Given that I don't work in the factory, I can't provide a detailed explaination. I'm sure someone on here is far more of an expert on plastic science than I am. But in use, the plastic on the handle is a lot thinner, causing the handle to bend when carrying the machine. The cord rewind causes the whole machine to shake from side to side and you can hear the cheaper plastic internal parts do not work smoothly together. The older machine doesn't have this problem - the machine stays complete still when winding the cord in and the cord rewind is smooth. It also feels a lot tighter (for lack of a better word) fitted to the top of the machine.
The tools have also deteriorated in quality - the dusting brush now has cheaper bristles instead of the high quality, soft bristles previously used. Same with the hard floor tool which uses to be made of horse hair. The tool adapater used to be made of hard, glossy, smooth plastic and is now made of a rough, matt plastic that is considerably thinner than the older version.
The overall build quality of the machine is less solid than it used to be. The plastic on the body is thinner and more prone to scuffing - the older machines seem to be made of higher quality, thicker and more rigid plastic.
I'm sure it's already been said elsewhere about the cheaper quality motor in the current machines too.
Until you've actually put both cleaners side by side, it's difficult to understand just how much the build quality has deteriorated. Nothing to hinder the performance of the machine, but certainly noticeable. I don't think Numatic are alone in this though and I don't think it's restricted to vacuums. Everyone is cost-cutting to keep their prices low with rising production costs - without prices going up, it's envitable that cuts would be made somewhere.