I haven't seen this mentioned, but evidently the reason there is no Micro SD slot is to prevent a split in memory options and the confusion that comes with it.

See: http://www.androidcentral.com/why-nexus-devices-have-no-sd-c...

Though, I suppose they could develop some sort of solution that manages the split for the user so you can expand the memory and never worry about what it saved where...

All that said, I definitely prefer large internal memory over having an expandable memory slot... If I'm forced to make the choice.