I've spent spent close to a decade working in Enterprise software, first as a developer at PeopleSoft, and afterwards as an implementation consultant. During most of this time, I have wished there was some way to convince all these big, predominately Windows-based shops that there was something better available. But "Apple" is a dirty word in most large corporate IT departments, and Apple has never really seemed interested in challenging that. Old ideas persist long after they are no longer supported by facts. The fact that OS X is a solid Posix-compliant Unix which runs Microsoft Office, supports Windows printing and file sharing, and has virtually no impact from viruses or malware doesn't seem to hold much sway even when it is known. It is sheep mentality at its worse, but there it is.
Large corporations are not known for encouraging individuality, and no decision is ever made by a single person at most large companies. I think Heinlein's description of decision by committee is spot on: He described a committee as a beast with multiple heads and no brain. Any committee is less likely to reach the right conclusion than any individual member is. The whole is considerably less than the sum of its parts in this context.
Most of places I've done work for also balk at even hearing the term "custom software"; bizarrely enough, they are frequently willing to spend literally millions of their corporation's dollars to implement so called "Enterprise Software" - software to handle some set of tasks less efficiently than what they could have had by hiring a couple good Cocoa developers for a month. These projects often fail, and rarely do they come in on-time or under-budget, even when the schedule and budget are luxurious. Despite that, suggesting to a large American corporation that they develop in-house solutions in Cocoa would be openly laughed at. "It's not Windows" has been a sufficient argument against that idea for well over a decade now.
In the short term, I do not see the situation changing, but if the iPhone sees any serious penetration into the Enterprise market (and it certainly seems poised to), it could expose a lot of people to just how awesome Apple's development tools are. Shops that want to develop custom iPhone apps will have to buy some Macs, and will have to hire or train Mac-savvy developers. Like a benevolent virus, a love for Cocoa tends to be infectious, and some hands-on experience with modern Macs might just disabuse some of the Corporate IT drones of their outdates ideas about just what a Mac is.
I've worked on projects where handheld clients to ERP applications were being implemented. Though I've never been directly involved with the mobile implementation work, I have been involved enough to see that the offerings tend to be expensive, not particularly intuitive or easy to use, and often require you to hire the vendor's consultants if you've customized your system at all (and everybody customizes their system). In my experience, I can't recall having seen a mobile client to an ERP application whose functionality couldn't be replicated in a couple of days for the iPhone.
I would conservatively guess that a company willing to standardize on the iPhone OS and do custom development for their mobile needs could reduce the cost of their mobile implementation in half. Savings of 90% or more are absolutely not out of the question.
We do live in interesting times.