How much traffic do you think they actually lose by not having Nissan.com? I would have thought as soon as someone looking for Nissan cars visits that URL, they would realise it was not the right site, then try the ccTLD version i.e. Nissan.co.uk, or simply search "Nissan" in their search engine of choice.

It's a bit like Google AdWords - some choose to bid on their own brand keywords, but are they actually gaining incremental visitors, or just spending budget on acquiring traffic that would otherwise arrived for free anyway?