The argument is (partially) that you can't plant your iPad and have it grow into 1 million new iPads that you then sell to undercut Apple. Monsanto is arguing that the law needs to be considered specifically (differently?) for the case of self-replicating technologies since if the patent exhausts after 1 generation then the next year a customer could come on the market with millions of copies of their product. Software / book publishing business models dealt with this same issue via copyright that kept customers from reselling millions of copies of their product after buying it. Copyright doesn't apply to genetic code though.