get_posts('post_type=post&numberposts=-1')
and the
get_posts( array(
'post_type' => 'post',
'posts_per_page' => -1
) );
Are they the same?
Yes they are, the first form is internally converted into the second. IMO you should not use the first form as it is a relic to the days wordpress DB structure was much simpler. Today I am not sure if you can even achieve all the things you can do with the second form by using the first.