That's missing the point I'm afraid. What I meant was that the operation of the AI itself necessarily involves modifying its own "source code." The act of (generalized!) thinking itself is self-modifying. An artificial general intelligence is capible of solving any problem, including the problem of artificial general intelligence. And the architecture of most actual AGIs involve modifying internal behavior based on the output of thinking processes in such a way that is Turing complete. So even if you didn't explicitly program the machine to modify its own source code (although any efficient AGI would need to), it could learn or stumble upon a self-aware, self-modifying method of thinking. Even if it involves something as convoluted as using the memory database as a read/write store, and updating belief networks as gates in an emulated CPU.
You put source code in scare quotes. Most AIs don't literally modify their source cor, they just adjust weighting .ir whatever...essentially data.
Vincent Müller and Nick Bostrom have just released a paper surveying the results of a poll of experts about future progress in artificial intelligence. The authors have also put up a companion site where visitors can take the poll and see the raw data. I just checked the site and so far only one individual has submitted a response. This provides an opportunity for testing the views of LW members against those of experts. So if you are willing to complete the questionnaire, please do so before reading the paper. (I have abstained from providing a link to the pdf to create a trivial inconvenience for those who cannot resist temptaion. Once you take the poll, you can easily find the paper by conducting a Google search with the keywords: bostrom muller future progress artificial intelligence.)