PhDs are all equal in theory. However, in practice, the awarding body and the subject of the PhD definitely make some PhDs worth more than others. One only needs to look at recruitment patterns to see Oxbridge generally recruit Oxbridge PhDs, the UoL general recruit from UoL PhDs, then 'new universities' generally have staff who achieved their PhDs at 'new universities', and so on. This is the biggest indication that PhDs are not all the worth the same.
I chose a lower ranked uni in favour of Cambridge for my PhD - I now come to realise that the selling power of my PhD, particularly at international level, is much lower than if I'd studied at the latter.
It's a shame we don't have gradings for PhDs because some people do pass with flying colours and others just scrap through.