Hey wait a second, how come the SRD says this? (Under "Types, Subtypes and Special Abilities")
"Using a spell-like ability is a standard action unless noted otherwise, and doing so while threatened provokes attacks of opportunity."
It is duplicating the description in the MM, and does *not* say "unless noted otherwise in the ability or spell description."
That means that the default position is activated, IMHO. Enlarge Person as a spell-like ability takes a standard action.
[edit: ah, I have found it: in the PHB equivalent under "Magic Overview". That puts it back into "as per the spell" but then raises the question of my previous post - why post "1 standard action or like the spell or ability" if all spell-like abilities duplicate spells? Why not just say "as per the spell, unless described otherwise in the ability"?]