oops .... forgot to change the oil

Oil should last virtually forever unless it is damaged by heat or contamination. It can get dirty to the point that filters clog, rust preventatives give out or it goes acid. If you avoid cold starts and use block heaters as much as possible it helps with a lot of things. Modern engines are better sealed and cooled than they used to be so environmental contamination and heat damage are greatly reduced. It is a good idea to check your oil still and look for water as well as checking level but other than that I don't think that there is any harm in going with the manufacturer's recommendations. Even those are generally based on worst case scenarios. In my opinion more frequent changes just increases the chance of something being done wrong and adds to pollution. Oh, it does help add a lot of profit to some garages.