I have recently bought a fruit tree called Patio Apple/Pear Tree,the guy at the Garden Centre claimed that it is a Dwarf Apple tree with a Pear Grafted onto it.
Does this sound right to you?
Also if it's true the apple and pear should pollenate each other shouldn't they?
You can buy mixed trees so that bit sounds fine but not sure about the pollination as apples normally need another apple froom the right group, and pears another pear to pollinate them (unless they are a self fertile variety of course!) Not sure if this helps you or not really!
A trick that gardeners like to perform from time to time is to graft several different cultivars onto the same rootstock. You would then have, for example, different apple varieties that can pollinate each other. It's a method of producing fruit in a small space. It's called a family tree (good pun). A quick internet search reveals a few examples of apple and pear grafting, but if you want fruit I would recommend buying two sure fire compatible varieties of the same genus. They need to flower at the same time too!