I'm considering switching from DSLR to mirrorless and have been researching the micro four thirds (M43/MFT) and Sony's new Alpha 7 (A7). While Sony hasn't released many lenses for this new system, many are saying the lenses will be much larger and heavier due to the sensor being larger than MFT, despite the Sony being the same size as popular MFT cameras (Olympus OM-D E-M1). Lens size and weight is important to me since I'm wanting roughly APS-C quality or better in a much more portable system.
How are people making the assumption that the full frame sensor of the Sony A7 will net larger heavier lenses to be equivalent to MFT versions? Does this pertain to width, length, or both? Would it be possible for Sony to eventually release smaller lenses similar to the Olympus MFT system without cropping the full frame sensor?