It takes a while for each Android version to make it onto devices. Jelly Bean will likely be no different.
I personally see this as a benefit, not a problem. This way, developers can take their time building in support for new OS versions into their applications. That way, when ICS devices start really getting onto the market in large numbers, most apps will be compatible. The same will be true of Jelly Bean, and all OS versions that come afterward.
You have to remember, not all consumers like being on the bleeding edge like us techies. Most of them aren't willing to sacrifice for the latest and greatest. Most of them wouldn't want a Jelly Bean phone or tablet the moment it came out, because not many apps would support it.