Yeah that was why they bought Arrowpoint and Aironet and Scientific Atlanta etc.
I'm sure there are some acquisitions motivated purely by the desire to eliminate competition, but I think they are fewer and farther between than you might think. Most of those kinds of acquisitions are not significant competitors. They are usually just bothersome gnats in the marketplace who happen to have some desirable patents and technology. Now if they bought someone like Juniper or Checkpoint or Aruba, then I would agree with the statement.
Cisco's IPS/IDS has long been trailing the market and in sore need of a competitive facelift. I can't recall the last time I heard a big enterprise seriously consider Cisco in that space. It's been years.