Is there an industry set time between a DVD being released and when it gets reduced in the shops? Four months? Six months? I ask because I never buy full priced DVDs and virtually always wait for them to come down.
Reducing DVDs?
Nothing set that we're aware of. There are, arguably, conventions rather than guidelines or rules or anything, but it really depends on the seller, any discounts or offers which may be offered by the distributor, and ultimately the popularity of the individual release.
Oh, and time of year. Pricing almost invariably goes up around Christmas and 'sale' times.
I never buy DVDs, unless it's my most favouritest show everer.
You ARE me, and I claim my £5. (Not yours though.)
I have several home made movie DVDs on special offer at the moment.
Do they come with counselling? 
Yeah, it's on the bonus disc.
But its an Easter Egg to make you even crazier by the time you find it