If you rent servers or buy colo from anyone else, you can ALWAYS renegotiate all prices based on a new level (if you've got a cage and want to expand to a floor, it becomes a negotiating point; you don't get stuck paying the higher price on that cage and a lower price on the floor.
Until very recently, the only Amazon discounts I've ever heard of were the Reserved Instances (which really only makes sense once you're familiar with your needs). Inability to negotiate pricing is one of the main reasons a lot of consultants still go with non-Amazon options -- the client sees the list pricing for EC2 and knows what markup you're applying, vs. another option (or your own cage/suite/floor/facility) where you can consolidate all the charges.
There are a lot of resellers of various services with different levels of value-add. The reality of the hosting business is that different providers give different levels of service, and in a lot of industries you do not want your customers to know your costs, so breaking it out as a separate line item isn't always optimal. Businesses actively try to avoid their product being viewed as a commodity.
There are also purchasing people in big companies who are paid to negotiate down quotes. If you tell them there is only one price for EC2, and they can't get a 5% discount for a large order, they will in some cases have a perverse incentive to go to a more expensive (list price) provider who will give them a discount (so they appear to be doing their job), even if the total price ends up higher, or the service ends up worse. This is one of the many problems with enterprises.
I'm not saying which model is better, but it's definitely a factor with some clients.
In case anyone believes this comment (that "until recently" there have even no price drops), I will throw in an alternative anecdote (as I'm at a restaurant and am not interested anyway in digging up alternative evidence: readers can do that themselves), Amazon has decreased their prices for all kinds of things many times; bandwidth quite often, servers a few times... I actually find myself misquoting Amazon's prices in conversations often due to having lost track of random price drops.
The one thing that hasn't dropped is where 99% of my costs are: the price of a PUT to S3.
We're talking about two different things -- price drops vs. discounts.
They drop prices across the board all the time. They don't do individual negotiated prices at time T which are different for one customer vs. another customer. (they just started doing this a few months ago, in the form of offering special services to some customers but not others, and now in terms of volume pricing discounts).
All hosting providers drop prices over time (mainly by increasing the amount of RAM per server at the same price, vs. dropping the pricing of packages) for some things (and tend to raise for power, cooling, and physical space). But everyone except Amazon usually also does individual negotiation of prices.
Amazon do negotiate individual prices in some circumstances.
I'm not entirely sure what circumstances it takes to make them negotiate, but the discounts I've heard about are significant. It doesn't seem to be based on the size of the deal though.
The only times I've heard of this were GovCloud (which costs more, but includes a lot of extra service) and the recent announcement of volume based pricing (which is sort of individual in a way).
Dropbox, Heroku, and Netflix would be the authoritative data points, I think. I've heard "won't do anything custom", but I never really pushed to find out about discounts. Even if they do exist, they're nowhere near as common as with every other provider (where either you get a marketing deal discount, or can just get a discount for the asking, especially early on, or as you grow).
Until very recently, the only Amazon discounts I've ever heard of were the Reserved Instances (which really only makes sense once you're familiar with your needs). Inability to negotiate pricing is one of the main reasons a lot of consultants still go with non-Amazon options -- the client sees the list pricing for EC2 and knows what markup you're applying, vs. another option (or your own cage/suite/floor/facility) where you can consolidate all the charges.