I suspect the thinking is, "If it doesn't say it's a spell, it's not a spell" combined with "Why would something that's not a spell be a spell?" -ignoring the confusion over abilities that look, sound, and smell very much like spells.
But wouldn't the designers know it might be an issue? Why not answer the question in the actual text."Spell Like Abilities: These abilities are considered spells for the purpose of counterspell, dispel and anti-magic shell. If the level of the spell must be determined, use CR/2." Or whatever the appropriate mechanics would be (I'm just making stuff up off the top of my head). My point is: why isn't this information in the book that introduces the new mechanics?
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