All these arguments about BBC should have just used jQuery are non-starters.
There are plenty of off the shelf website production systems on the market, for instance. If you think a JS team should only ever use a library, I presume all your websites are created in Drupal using built in templates.
Software you produce yourself does exactly what you want with no bloat. jQuery is excellent, but there will always be gaps in it for any given organisation. Additionally there will be bloat. Sizzle is fantastic software, but my guess (based on actual observations) is that 90-95% of the selectors it is given in the wild are of the '#someid' or 'tag.classname' type. These can be handled with 20 lines of code, but Sizzle is closer to 1000. Many libraries contain code to support use on both standards compliant and quirks mode web pages, but if you only ever code in one of these, that extra code is useless.
Then there is the issue of dependency. External dependencies are one of the weakest points of any software product. You can't directly fix bugs or fill functionality gaps, so you must either branch the product or work around the issues. Both approaches cause pain when wishing to upgrade to the next version (a decision which may be forced on you by the supplier's support levels) by either having to re-engineer the patch or check compatibility of the workaround. Yes, you can submit bugs or patches, but you cannot control when, or even if, these will end up in a released version. Even if your bug is fixed, you may still have to re-engineer your codebase, because the fix may break your workaround.
If your organisation has the resources to produce a piece of software itself, it should. That organisation will end up with a product that does exactly what is required with no bloat, will avoid the pain of external dependencies, and will have team of people on board which provides a centre of excellence for that technology. For organisations much smaller than the BBC, these benefits will probably outweigh the small cost saving of using a JS library like jQuery. For the BBC, it's a "no-brainer".