I have always assumed that the 7200.11 and ES.2 drives had the same hardware. (Of course not all 7200.11 drives are the same, so my belief has been that each ES.2 drive was the same as some 7200.11 drive.) Note the word "assume". I have no evidence but common sense.
Why two lines for the same device? Well, they are not identical: slightly different firmware (ES.2 has time-bounded error recovery, required for RAID), different marketing, different warranties. The key goal is to achieve "price differentiation". This is the goal of any producer in a commodity business.
When products are commodities, their price reflects the cost of production; if some vendor's cost of production is high, he cannot even get that without losing market to lower-cost producers. Price differentiation allows a vendor to start charging based on the value to the customer rather than the cost of production.
There is a very good chance that Seagate would do something to prevent ES.2 firmware working in a 7200.11 drive. Preventing the opposite isn't very important but might be a side-effect.
This is also why Seagate probably makes it impossible to put the 7200.11 drives into a mode where error recovery is time-bounded.
What surprises me is that even ES.2 drives don't (always? sometimes? as often as 7200.11 drives?) work well in RAID setups. This means that the problem is not just the traditional unbounded error recovery time. If there is a single underlying problem, and the ES.2 problem is the same as the 7200.11 problem, then things are really grave for Seagate. They have not solved it in a year!
