This is necessary, as we can't prevent setuptools from respecting any such eggs, therefore we need to respect them in order to maintain consistency. However, we don't normally install any "install_requires" eggs into the source tree root dir.
Note that using "whatever version of python the name 'python' maps to in the current shell environment" is more error-prone that specifying which python you mean, such as by executing "/usr/bin/python setup.py" instead of executing "./setup.py". When you build tahoe (by running "make") it will make a copy of bin/allmydata-tahoe in instdir/bin/allmydata-tahoe with the shebang line rewritten to execute the specific version of python that was used when building instead of to execute "/usr/bin/env python".
However, it seems better that the default for lazy people be "whatever 'python' means currently" instead of "whatever 'python' meant to the manufacturer of your operating system".
