iOS gives you direct hardware access to the device so you can do photo editing, video editing, music production, high resolution high frame rate gaming, and dozens of other device-local tasks. How does a series of glorified web browser Googlebooks compete with that?
No one has written the next Photoshop yet, but the apps that need NaCl are using it. The SSH client, for example, which works great and actually lets me get a lot of work done from my Chromebook without even turning on developer mode.