ethernet - Difference between link-aggregated 10x10GbE and "True" 100GbE

I'm reading on 100G Ethernet and came across this article by ADVA. On page 2, top paragraph (before "Spectral Efficiency"), it compared link-aggregated 10x10GbE and a "true" 100GbE and says

A true 100GbE path between two core routers will produce 100Gbit/s of throughput, more than twice the real performance of a 10x10GbE aggregated link.

But what is the real difference between them? As I understand the "true" 100GbE also put 100G on 10 different wavelengths each carrying 10Gb/s (some cases 4x25G), how is that not link-aggregation? Is the difference not in the physical layer but how you code the packet onto the physical layer? Is there a reference how this is done?