Of course the BBC should support screen reader users, and of course it should keep producing quality programming which could not otherwise be made.
This is not a matter of providing something people would otherwise not have access to. Safari 1.3 users would have been able to use the site without Glow, but their experience of it would have been a bit degraded. No doubt less so if a fraction of the time put into developing Glow had been put into finding the best ways to mitigate the page degradation. Safari 1.3 may have had its problems but it is essentially a capable rendering engine for the kind of page functionality the BBC uses. After all the BBC is hardly pushing the envelope for HTML & Javascript technology, nor does it need to in order to deliver its content.
I don't see that there is any serious business case for this amount of development to support this level of refinement for such a small group of users. The fact is that developers are in a luxurious position of following what appeals to their vanities rather than delivering value for public funds.
Someone mentioned the team was small. How many of them are contractors vs permanent? I bet they are not all permies. Even so, one permanent salary for two years is a heck of a lot of money to throw after a project replacing something which is 'good enough' and available for free.
Can you point to pages or features on the BBC site which, without the use of Glow, would render content inaccessible or completely unusable to Safari 1.3 users if jQuery had been used?