San Diego is pretty much 68 to 72 year round. In the summer it might get a little warmer and in the winter a little colder on select days, but it's a pretty tight range.
Speaking as a San Diego native, it does get colder than 68 and it definitely gets warmer than 72. Summers can get a little hot when the Santa Anna winds kick in. However, compared to vast majority of places on earth, our weather is better.
Ok, fair enough, the range is more than 68-72, but still pretty tight as far as places on earth go: