I tend to consider haikus those poems that feel like a haiku, so if the form differs a bit but it still resonates like one, then that's a haiku for me. and as the other person said, there are different forms of haiku, besides the traditional form that you mention (and it's about on's NOT syllabels). and modern haikus don't follow that norm, and don't follow the usual way of construction either. you can read about all that on wikipedia: [link]
there are different forms of haiku. at least fifty that i know of. also it depends on the language.... the 5 7 5 rule is traditionally meant for on, not syllables... though I agree it could confuse those who are unaware of such facts. Sorry, my mother is an english professor. I tend to get protective of the literary form.
on is a combination of sounds. it makes up the japanese alphabet. such as ka, ki, ku, ko, and so forth. in japanese you write with sounds. take the name hikaru for example, it's made up of hi, ka, and ru. therefore instead of six letters there are three hirigana or characters. so if the haiku is written in japanese it is write with five on in the first line, seven in the second, and five in the last. Of course there are other ways to write the lines, but there are always three and the last must always end with a sharp word, something cutting compared to the rest of the words. They are traditionally about nature as well. Haiku is a very complex poetic form and that is why there are very few true masters. Though there are many modern day interpretations that don't use nature as their base, I've always been fond of tradition. sorry for the lesson... i just REALLY love poetry. My mum was drilling me in it since I could crawl it's become automatic.