As to the person wondering about discount rates, there are pros and cons to that. The pro, as mentioned, is not maintaining a separate list of hard prices. The immediately obvious con is figuring out later, say 6-mos down the road, when products prices' may have changed, just how much that product cost under that promotion.
You're talking about a different data set, that information is in your sales ledger.
I'd say it adds a lot to the flexibility, you can then treat the discount rate as a "what if" scenario - granted you'd have to create a view onto the data which works out the actual selling price after discount, then join that view to your reports (not so difficult), but think about sales forecasting and margin calculations (remember margin is a product of COGS, NOT current selling price, which to mind mind is irrelevant in this context), you'd have hard and fast historical data about what sort of discount generates what kind of extra demand pretty simply available - then you could start forecasting with different discount rates and tailor the promotions accordingly.
You can do this with the existing model, granted, but it makes it much more difficult. Also the existing model doesn't lend itself well to fast setup, personally I'd be looking into categorising products (if only by margin) so they can be treated en-masse in "promotional groups"