Given your original parameters, my point still stands. If you're looking for a laptop "replacement" then obviously a "laptop" is going to fulfill that need.
You might say that a current laptop can do this and more. The "and more" part is the issue because it ends up causing the average user more trouble than it's worth; seriously, talk to them. They still have issues with anti-virus software, paranoia about getting a virus, performing updates, anxiety resulting from worrying about what might happen if they do/don't update, resolving issues that result from updates, resolving issues that result from not updating, what to do when when it runs slow, drivers, handling files, dealing with the inevitable mess their system will be in after a year or two of use, etc.
First paragraph - second paragraph + fast boot + good battery life = massive market of potential happy users. Again, I don't know if Chrome OS will succeed but the market's there waiting for something better.
2) JavaScript speed.
When tablets browsers catch up to the desktop on those two things, I'll consider using a tablet for more than just a comic reader (all I use one for now).