The M-series aren't blades
The M stands for "modular". The B_Series (which according to the story is what customer are asking for) are their blade offerings. The C-series are their stand-alone rack boxes.
This all makes sense to me since the M-series were a weird hybrid of both, but lacked the features that made the others desirable. The M-series only put 8 wimpy servers into a 2U machine, yet required the XFP connectors that the B-series chassis used. It was a weird middle-child product that didn't really fit into a specific role. They might've been able to save the line if they used common parts as the C- and B- series (EG, a 1- or 2-slot blade chassis that used standard network interfaces)