Paul,
I think part of mould/mildew problems is a combination of not using the recommended amount of detergent, and not leaving the door open. However I have to say that my nana, who uses two tablets of detergent as do I in similar water conditions - she only lives a 5 minute walk round the corner, rarely washes above 40*C and never closes her washer door, but is starting to get mould on the seal her almost 2 year old WF340 and it can smell musty inside. I suggested to her that she did a 95*C maintenance wash and voila her machine was right as rain again... so I think there is a link between lack of high temperature washes and build up of mould mildew. One of my friends has a new Miele, approximately the same age as mum's and they never wash above 40*C, and again even with leaving the door open their seal is beginning to cake with mould. I can add to this by saying that we regularly use 60*C or above at least 3 times a week for bedding and towels, and we've never had mould problems. To add more confusion though we always had mould issues with the Bosch, even with high temperature washers so it probably is machine-, habit-, water-, geography- and detergent-dependent as to whether mould problems occur or not.
Thus the easy way for people who would otherwise get these problems would be to run a maintenance wash every month if hot washes aren't used as regularly as they should be - even the manual for my washing machine states this so there must be some element of truth in maintenance washes.
I forecast this to be an increasing problem with us being urged to wash at even lower temperatures nowadays, and having seen such problems for myself and seen the amount of posts on the internet I think you're probably one of the lucky ones, along with myself, who've never experienced mould problems personally in the machine purely from following good habits.
Jon