The 2.5x markup is pretty typical, though in my experience it's closer to 2x on average.
As Dave mentions, fast-moving consumer goods (FMCGs) can be much less, slower moving "luxuries" much more. Here's another way of explaining it:
If an item costs $1 to make, and you sell on for $1.50, you're making 50c profit. Sounds good, until you realize that if your costs increase by 10%, you're now down to just 40c profit. That's a 20% hit!!
But if you buy at $1 and sell at $2, then a 10% increase only costs you a 10% hit.
Of course, if you could sell for $3 it's only a 5% hit, but then you leave loads of room for competitors to undercut you.
So natural selection tends to weed out those charging too little or too much, and a 2x markup (or 50% profit margin in business speak) becomes the norm. Cost increases are then manageable: Could be inflation, minimum wage increase, oil prices, exchange rate fluctuations, stock loss/returns, bad debt, etc etc. It happens a lot, and you can't always pass on the increase to the customer. That 2x markup helps you weather the storm.
To use Dave's example: cost of $50, sell at $78, profit $28. A 10% cost increase would wipe out 18% of your profits. Not great, but I've seen worse!
However, I think the 60% distributor markup is a bit on the low side. Everyone in the channel plays the same game, so they tend to double-up as well. (Retailers are even worse - they'll try to squeeze the pips out of it!)
If you're looking to get a product onto the shop shelves, it works out to about 10x the ex-factory cost:
Say it costs you $1 to make, so you'd sell it to a distributor for $2. They'd sell to a retailer for $4, and it'd be on sale for $10 (inc sales tax). It's really that bad, and it also helps explain why there is so much badly made stuff out there. The folks at the bottom of the food chain really have to save every last cent to stop it multiplying up.
A better strategy is to find a niche market. and make what the customer wants. If you're trying to sell something, it'll be hard work. If you've got something people want to buy, you can name your price.