This 29p thing is just a publicity stunt by Amazon to coincide with Apple's new price structure.
Just 0.002% of Amazon's tracks are at the 29p price-point, and no doubt only temporarily, because after the record industry and artist cuts, there can't be much if any money left.
The record industry has long wanted variable pricing in iTunes, but Apple has pushed to keep flat-rate pricing, which is simpler all round.
Finally though, in return for the Record Labels allowing Apple to sell DRM-free tracks, Apple has given in and bowed to the variable pricing conditions.
It's no secret that the Record Industry doesn't like Apple's dominance in the market, so giving preferential treatment (lower-prices and DRM-free) to alternative retailers is seen as a way to reduce Apple's majority market share.
The way this is being reported by the mainstream media you'd think Apple are deliberately increasing their prices at exactly the same time as Amazon is lowering theirs.
In reality, Apple's pricing is governed by the Record Labels, and Amazon's temporary promotional price on a handful of tracks is a well-timed, loss-leading, publicity stunt.