Not sure where you have been for the past century.
1.) The assumption that a vendor knows more about their own products is only marginally true, collectively i'd say they actually know less than their customer base. If they knew more then they would find all the bugs, and back doors to their products.
2). Once you select a supplier in the cloud, how easy do you think it will be to move.....Really....baring in mind our industries history of locking in customers whilst paying lip service to open standards.
3). Realistically how safe do you think your data will be from accidental exposure, hacking, requests from the DoJ for disclosure to the hosting organisation. A hosting provider will represent a massive target for hackers, why go after a single company when you can get 10.
4). Yes the telephone network is a cloud, and not very secure, why do you think governments use separate networks, or overlay their own security on top of the channel.
5). Banks are not clouds they are store and forward messaging services (Think about it) that overlay their own security on top of public networks, who have a vested interest in keeping data secure, and they aren't too successful at that.
6). As UK Gov. has just found out some of the IT companies are so big, they can dictate to you the terms of business, and don't really care about you as a customer, even when you spend billions with them, you still only represent a fraction of a % of their business, so once they have you why should they care about your service, baring in mind the costs of reversion, or migration to another supplier, who will by the way be offering "industry standard competitive" solutions, or lowest common denominator.
7) Clouds make sense for small business, Amazon & eBay work well. For more serious users, the bigger you are, the less sense it makes, better to operate your own cloud.