I don't think a suit is necessary for positions that aren't quite senior or managerial. I can offer some thoughts having worked near IT as a software developer.
As an Australian who has worked as a software engineer in three companies so far, personally I've always gone to job interviews with a collared shirt and nice pants, but no suit and tie. The same has been true for many other people I've seen applying.
Australia may be more laid back (a number of people I know here work every day in a tee-shirt and jeans), but in my experience I think it is not uncommonly expected that you try and dress to a higher standard than that for interviews. Historically in white-collar positions, I think people read it as a statement of your sincerity and values, but I'd also say this is rapidly changing.
I suppose the question is whether you're being interviewed by and meeting with people who are concerned with appearances and are 'old fashioned' like that, or with people who will prioritise your abilities and suitability for the role.
Personally, I'm not sure if I would be comfortable wearing jeans to one, as you never know who you'll meet at an interview (I've been introduced/presented to upper management before as part of a tour), so I think there's a judgement call to make based on what type of company it is. On the flipside, perhaps a company or manager that judged you on your dress isn't one you want to work for anyway?
Either way, the choice is yours, but I like to play it a little safe.