If you feel around the margins, you can find exceptions for everything. e.g. You can cook a fish in a dishwasher. But while anyone can modify a toaster to do wild things, they aren't designed to facilitate that and it isn't a mainstream thing to hack your toaster.
PCs are hackable by design. It's a perfectly mainstream thing to build your own PC from parts. Hacking toasters, on the other hand, is not mainstream. Best Buy sells toasters, but not parts for toasters.
I personally wouldnt draw the line between information appliances and computers at whether the manufacturer actively blocks you (as Apple and John Deere do), but rather at some combination of what the intended purpose is, and whether hacking and customization is considered mainstream or fringe.
Hacking toasters and dishwashers and microwaves and refrigerators is possible, but fringe. Hacking cars and houses is mainstream.
