I think the only time it is justified is if you are selling something as grazing land and it's your entire view and the purchaser swears they want it for grazing and they only pay grazing price for it. In other words, the uplift isn't there so they [size=78%]share in the money made, it's set so that the land remains unspoilt. For that to work, the uplift percentage would need to be set so high that any development would be unprofitable. Preferably also retaining a ransom access strip of land. [/size]
The greedy ones I think are ones where it is set at a level that would make development still just about doable, but mean the original owner trousers a large part of the benefit with no work, esp if the site is not affecting their own home etc. that's just greed and I wouldn't enter into a deal to reward someone like that.
In response to the OP, these clauses are legal and fairly simple to enforce by the original owners so would suggest if the terms are not acceptable from your perspective, try to negotiate it down or away or walk away and find land without such a clause.