Good objections, but outdated
"it cannot support heavy data transactions dynamically with multiple UI present"
With HTML5, that's possible.
"If you freeze one browser pane, the whole app is gone."
Not in modern browsers that use separate processes.
"Lose your network, your browser is toast if it requires connection to a server."
Not with HTML5, which has capabilities for syncing after the connection is re-established.
"I also feel that while tablet and mobile applications are great, they do not have the ability to really do heavy efficient work without a full keyboard and mouse."
I agree, but what we're seeing are docking stations that provide that functionality.
These are the changes that have made the difference. Browsers are better, HTML5 is better, and with the pending docking stations, there is no reason to use a PC except for extremely resource intense tasks (multimedia editing, development, number crunching, etc.) which are very niche tasks.
J.Ja