In these sorts of situations its best to think of the sort of response people give when talks of how long BBC One have been using their current branding, or how making UTV just the same as ITV will lose them millions of viewers. Whilst it's always nice to have xyz look to the surrounding brand, the reality is people will continue watching as long as the content they want is there. I firmly believe the same applies to people looking at pres sites too - as long as the design itself remains functional, the content of the site is much more important to people.
Indeed you can just look at one of the most common places people go to find presentation content now, namely Youtube. The Youtube site visual design still looks like a turd that's been through a blender before being thrown against a wall and has changed little for the past decade - but it's massively popular because there's such a massive amount of content there.
(Yes, I realise these views probably aren't the most popular in a community dedicated to branding and presentation... but they're realistic!