If they require no components to cast, why do they take a standard action to use (other than game balance i.e what's the in-universe reason?) Also, what does it look like when a creature is casting a spell like ability? I'm guessing they just stand there and seem to be concentrating until the spell is done.
It's the same idea as if you use metamagic feats to suppress all of a spell's components. There's still a mental process involved, where the caster summons up the mana / ki / psionic energy or what have you, shapes it into the spell(-like) effect, and cuts loose. That takes enough effort to (normally) count as a Standard action, and at that one that normally provokes.
As for your second question, this might help answer it:
Although this isn’t directly stated in the Core Rulebook, many elements of the game system work assuming that all spells have their own manifestations, regardless of whether or not they also produce an obvious visual effect, like fireball. You can see some examples to give you ideas of how to describe a spell’s manifestation in various pieces of art from Pathfinder products, but ultimately, the choice is up to your group, or perhaps even to the aesthetics of an individual spellcaster, to decide the exact details. Whatever the case, these manifestations are obviously magic of some kind, even to the uninitiated; this prevents spellcasters that use spell-like abilities, psychic magic, and the like from running completely amok against non-spellcasters in a non-combat situation. Special abilities exist (and more are likely to appear in Ultimate Intrigue) that specifically facilitate a spellcaster using chicanery to misdirect people from those manifestations and allow them to go unnoticed, but they will always provide an onlooker some sort of chance to detect the ruse.
Emphasis mine. This FAQ pertained to how one might answer an SLA (or spell with all components suppressed) with a Spellcraft to identify it, an AoO, or a readied disruption.