There is just a few Simple Check item keys which is a static list. There is no way to have custom key. So why not simplify/automate the process of adding a simple check items by having a drop-down box with list of available keys in the item add/edit form? And in addition to get rid of the return value type drop-down in this case, which by the way (return value type) is not even documented here

http://www.zabbix.com/documentation/2.0/manual/config/items/itemtypes/simple_checks

(e. g. no mention about icmppingsec[] return value type which must be float).