This seems to be implementation specific, depending on compiler, OS and memory controller. The standard is available at: http://www.jedec.org/standards-documents/docs/jesd-79-3d . It seems that if your controller is fully compliant there are specific bits that can be set to indicate interleaved or non-interleaved mode. See page 24,25 and 143 of the DDR3 Spec, but even in the spec details are light.
For the i7/i5/i3 series specifically, and likely all newer Intel chips the memory is interleaved as in your first example. For these newer chips and presumably a compiler that supports it, yes one Asm/C/C++ level call to load something large enough to be interleaved/striped would initiate the required amount of independent hardware channel level loads to each channel of memory.
In the Triple channel section in of the Multichannel memory page on wikipedia there is a small list of CPUs that do this, likely it is incomplete: http://en.wikipedia.org/wiki/Multi-channel_memory_architecture