Apple\'s iOS developer guidelines state:
3.3.2 — An Application may not itself install or launch other executable code by any means, including without lim
The concept of the differences between 'code' and 'data' has been discussed on SO before. Please see this answer: https://stackoverflow.com/a/642476/200696
From Apple's perspective, this ban prevents un-reviewed executable content from the app store. It would be trivial to create a program which is approved by Apple, and then downloads executable content that changes the pre-approved behavior.