This series of posts has been really interesting. At first I was dismissive and found myself disagreeing with a lot of the assessments but the explanations of why one language's approach is better from a beginner's perspective can tell us much about better ways to teach programming.
You don't have to. The 2nd argument is optional and defaults to IO::SEEK_SET. (Source: http://www.ruby-doc.org/core-1.9.3/IO.html#method-i-seek)