As with most things in life, all these thresholds need a huge amount of qualification and an idea of context before they can be assessed. There are different cut off points for various facets of VAT, for CT and for other regulatory concerns, but even here the danger is that they are far too generic to cover every business type.
There is a massive difference between the turnover of a low margin company and a high margin company with respect to their "size". For example a solicitors retains close to 100% of its revenue as "gross profit" whereas a currency trader may retain under 1% of revenues so may be turning over many millions to turn a small income. These extremes are quite clear cut, but when you look at retailing as a whole, there doesn't appear to be much distinction between different margin businesses which could range from 5% to 85%.
I guess the more common thresholds get round it by using the "any two of three" concept, but this does not mean that the attempt to generalise is remedied perfectly. Then again, unless there was case by case screening, which would be prohibitively expensive, this is probably the best fit.
Interesting that the fire safety threshold was mentioned earlier, since, as far as I remember, this one is definitely flawed. It seems to use the number 5 without reference to size or number of premises such that a company with five small shops and one member of staff in each must do five separate risk assesments, whereas one shop with four members of staff working in does not. Would surely be better administered on a staff per premises basis rather than per company.