See to my mind they aren't charging their daily rate, because the figure they use to calcuate, and the figure they charge for one-off care, is different. This isn't a debate about nursery pricing structures, though!
To my mind it's the same as a CM saying okay I charge £4/hour so over a normal day (8-6) I charge £40, which is £200 a week making it £10,400 a year (if you have an ongoing arrangement) BUT I take 5.6 weeks off unpaid (4 week plus BHs) so my annual rate is £9,280, which you can pay as a monthly figure of £775 (or £773.33), or a weekly figure of £180 (or £178.46 if you wanted to be precise).
That way the holiday itself isn't charged but the income is spread over the year.
Both are passing on the discount.
A true 'daily' rate would be the nursery/CM saying 'I charge £40 a day even when I'm not open for business'. Like a nanny with a weekly rate of £200 but does get paid holidays so the income is £10,400 a year.
All I'm saying is that sometimes you appear to be 'paying for holidays' when in fact it's built into the payment structure so you don't.