PureFlex != Flex Chassis
Okay... it was alluded to in another comment, but it should be made clear. PureFlex is not equal to the BladeCentre... though, the Flex Chassis is, arguably, so.
The Flex chassis is a 14-slot chassis, with a lot of I/O bandwidth, power and cooling, etc. It is 10U, but supports higher power and density machines, though it is not the most dense equipment IBM sells.
The Flex chassis is a component of the PureFlex, but PureFlex is actually a full integrated-package offering that includes servers, storage, network and management appliance.
Other components of PureFlex include:
Flex System Manager (FSM) - a single-bay sized appliance that provides a single pane of glass to manage the server, storage, network of the system... can support (currently) up to 8 chassis of equipment, and can also run the full Cloud Management Suite - SmartCloud - from IBM.
I/O Modules - these are the ethernet or fibre modules that would be installed in the chassis. They are designed with full redundancy and very-high thoughput. They also support east-west traffic so that inter-chassis traffic can work at backplane speed versus the network/fibre wire speed.
Chassis Managament Module (CMM) - like the older blade equipment, a management interface for a chassis-based hardware management, also can be installed in redundant pairs.
v7000 flex module - basically, a v7000 that fits in 4 node bays rather than in an external unit.
Compute nodes - xSeries or Power nodes in several versions, including single and double-wide nodes.
I have installed these already, and while there is always a few growing pains of firmware updates, etc. that are to be expected, the systems seem to be fine replacements... even if that is not what IBM had targeted them as (officially, at least) as can be seen by IBM's difficulty in getting their own support staff trained up in implementation services