Don't need to use Suzuki filters now, just parts 'of equal quality'. I emailed Suzuki GB directly a while back and asked the questions. It's all in a thread on here somewhere.
But yes, I understand what you mean, they use an oil change as a reason to void the warranty on everything else. As Andy M always says, warranties aren't worth the paper they're written on.
How's the chainsaw oil working for you? I don't think Scottoil is that dear really, I'm still on my first 500ml bottle I started years ago. Only done around 10,000 miles with a Scottoiler fitted bike in that time though.