goodroi - 5:59 pm on Mar 21, 2011 (gmt 0)
Using a robots.txt file from another site is not always a good idea. A robots.txt that is good for Site A is probably not ideal for Site B unless they have both been configured exactly alike and they both have the same objectives. I would encourage you to create a custom robots.txt file to best fit your site.
I am not sure that wordpress.com allows for robots.txt to be changed. I think you might need to be hosting the wordpress on your own site to do that.