I too did not understand why they were using a finite grid, the article seemed somewhat naive w.r.t. life, more a cute exercise for Hadoop...
As a side note, the links to a java applet to run through the patterns they found was a non starter for me, so I used http://secretgeek.net/gameoflife_.asp
I don't understand why they are using finite grids (probably efficiency reasons, but with the right data structures you could still implement it fast, see hash life).