You can never be too thin or too rich. (Although I don't think whoever came up with that had Nicole Richie or the Sultan of Brunei in mind.)
And in the world of backup, you can never be too fast. It is just not possible.
The premise of their approach seems to me two-fold: one, the DD880 is fast enough that it obsoletes post-process deduplication technologies; and two, that this speed is high enough that for the first time in-line deduplication will no longer be a bottleneck in the backup process for the vast majority of customers.
Now I don't entirely disagree with these arguments. For a long time I have been saying of a DL4206 and DL4406 when asked of performance: "They are so fast that I can virtually guarantee that they will not be the bottleneck in your backup process." At up to 2,200 MB/s, we can see that there are many opportunities for backups to degrade before the EDL becomes the problem: data must be read from disk, through a client, across a network, sometimes mediated by an database or application interface, to a backup server, meta-data must be processed, and then it must traverse another network before it is written to a target. There are so many obstacles here (including the presence of an OS, a filesystem, different disk architectures, etc.) that there is very little chance that the EDL will be a bottleneck. Certainly not for a single backup server or storage node or media server.