Dynamic array of Years
In order to get the output that you wanted, using array_combine will most likely be your best bet. You can simplify your statements pretty easily because variables are you friends:

$current_year = date('Y');
$date_range = range($current_year, $current_year+10);

form_dropdown('year', array_combine($date_range, $date_range), set_value('year'));


Addendum by @brettsantore

I think this solves what I thought to be a problem, the combining of so many functions. I ended up simplifying it a little more.

$current_year = date('Y');
$range = range($current_year, $current_year+10);
$years = array_combine($range, $range);