What surprises me, is that the letter leaves room for (mis)interpretation on the essential content:

“We have never viewed 30 September as a deadline, but have stated from the beginning of this process that the transition planning should proceed to whatever schedule the community sets” is clear and in line with what Mr. Strickling has publicly stated numerous times. It suggests implicitely that the contract will be extended if necessary to fit “whatever schedule the community sets”.

However, the bit “..please bear in mind that the United States Government will need sufficient time to evaluate the proposal and that all work items identified … will need to be implemented prior to the ending of the contract.” is not so clear.

We probably all assume that “the ending of the contract” refers to either 30 September 2015 or the end date of an (or the last of multiple) extension(s). 

That is probably a safe assumption, but I fail to understand why Mr. Strickling did not insert a sentence to make that absolutely clear to anyone. Something like: “…prior to 30 September or the date to which the NTIA will extend the present contract to fit the schedule set by the community”.