That is not really true. Most workloads can be executed in parallel. Pretty much all the field of scientific computing (would that be physics, chemistry, or biology) are typically quite parallel. If you are looking at database and data analytics, they are very parallel as well, if you are building topic models of the web, or trying to find correlation in twitter post, these things are highly parallel.
Even on your machine, you are certainly using a fair amount of parallel computing, most likely video decompression is done in parallel (or it should be). It is the old argument that by decreasing frequency you can increase core count in the same power envelop while increasing performance.
For sure, some applications are not sequential. Most likely, they are not the one we really care about. Otherwise, hire me, and I'll write them in parallel :)