The problem here is that the bulk of systems that end up with these Celerons will be the lowest of low end Dell and HP landfillers, for example, that not only have to run a web browser, email or office application, but also all the other bloated nonsense that these system integrators insist on adding in as a 'bonus'. Not to mention all the various things Windows itself performs in the background at the same time. A simple task like checking an email becomes, at that point, somewhere adrift of efficient.
The users of these systems may not realise things are going slow, but only because they don't know any better. I sometimes have to wonder if many people end up overpaying for a Mac further down the line because they have now formed the belief that Windows PCs are always that slow, regardless.