The truth is, we as members of the general public simply don't know these people at all... full stop. Therefore we cannot in all honesty put forward these very definite opinions as to the whole subject of their relationship. We can of course speculate all we want (and it's only human nature of course for the public to do this when dealing with famous people) about the ins and outs of the the entire subject, but we have to accept we do so without the remotest inside knowledge on the people in question - any why on earth SHOULD we have any inside knowledge.
Are there couples living near you who have been together for over five years and have yet to announce anything. Probably lots.... we all know of poeple like this. Do we sit back wondering all day long about what their plans are, if they are really suited, what their motives are.... of course we don't .... they are strangers to us... and its their business. They don't owe us any explanation as to their lives or plans. The same goes for William and Kate, two people who in reality are strangers to us, the public. We don't know them, they owe us no forward explanations at all.
He is royal, and she very soon will be, without a doubt. It will happen when it happens and of course we will all be excited about it, and follow every minute of it from begininng to end, because of their public profile, I think we just have to step back a bit from all the personal speculation about this couple...at the end of the day, it's their own business.