Is there no use for high temperatures in ovens?
There is lots of use for high temperatures. Especially pizza is the first thing that comes to mind; there is no home oven which can get to the proper temperatures for a Neapoletana (which are above 500 Celsius), but more is always better. 

Of course, the salesman will tell you what you need to hear to buy his product, don't listen to him. This still doesn't mean that you should only buy the oven with the highest max temperature; there are badly built ovens which claim to reach 300 Celsius but can't actually do it, in this case you are probably better off with a better quality oven with a lower nominal maximum temperature. It is probably best to compare reviews made by independent test organizations.