BA chooses to use the waterfall methodology in areas where there are a lot of requirements that can't be altered; where user communities are long established and the existing infrastructure is functioning at a level that can't be easily topped; and where major operational integration software has been built around an SOA foundation. "These are the 'big bang' areas where a tremendous amount of continuous integration is required and there is no room for discussion or testing of barriers," said Croucher.
-- from Where Agile development works and where it doesn't: A user story
Requirements that can't be altered? How is that a barrier to Agile? Every project has constraints.
Ditto for SOA and, in general, legacy software that has to be accommodated.
"... the existing infrastructure is functioning at a level that can't be easily topped ...." This smacks of arm-waving. But if there really is a waterfall process that ain't broke, not only shouldn't you fix it, you should tell the world about it.
"... where user communities are long established ..." This is the one real issue: the difficulty of explaining the benefits of Agile to people who have major economic and emotional investments in the status quo.
This article is a specimen of a certain genre of "even-handed", "objective", "above-the-fray" punditry: sure, there's a time and a place for Agile, but NIMBY....
P.S. If you follow the link in that quote to "waterfall model", you'll see this:
Alternatives to the waterfall model include joint application development (JAD), rapid application development (RAD),