>>The answer is that the IPad safari browser doesn't support Silverlight just as id doesn't support Flash

Yes, but OP says it has to run disconnected anyway. IMHO you need an extremely good reason not to propose a fat-client app optimized for the particular device.

One problem with choosing a WinCE device is that MS has broken backward compatibility between CE6.5 and CE7, and CE7 is not yet available on devices for prototyping or anything else.

Here we have a client starting from the iPad position. If developer familiarity is the major consideration then you'd need to persuade them to change device so they can use the system with which you are familiar, and the destination is still a big unknown. IMHO that would be brave for both client and developer. In such a case, IMHO the developer should consider changing their own prejudice (in its classical sense, not a critical term) to focus closely on what is best for the client, which seems to be a fat client app on a prevalent device, meaning iPad or Android IMHO. the fact is that these devices are outselling Windows Mobile by an order of magnitude, meaning that there will be plenty of developers keen to deliver what the customer wants if present company will not. When we can see a CE7 device it will become possible to consider that, but today it's simply not a reasonable option IMHO and nor is it reasonable to lock the client into CE6.x when we know it's being sidelined.