But the order of magnitude between disk and ram is so large that sequential versus random access on hard drives doesn't matter that much in comparison.
Well, it depends on the hard drives you're using, and the exact access pattern, but sequential access to disk can be even faster than random access to RAM.[0] This of course doesn't really matter to average Joe, since he has little influence on how data is read from his disk. But if you're say, a database developer, it does matter quite a bit.
[0] http://dl.acm.org/citation.cfm?id=1536616.1536632