Ok, before we go through the long discussion on "dice-based vs card-based randomness in games" and "luck^1 vs luck^2",
here's the previous thread on this topic. I appreciate this may fall under tl;dr though, but I'm linking it for those who stick with the reading.
With that out the way:
1) Some people feel edgy about rare minerals (not gems - those are 100% drop) as they can only see a fraction of the clusters at a time and there is tangible risk of not getting anything from these clusters as they are small. But as Girlinhat points out: you get way more from caravan delivery anyway. Mods... are going to have to undergo major re-writes if they were relying on rare mineral drops for something. But then, that behaviour can be kept by turning those rare mineral clusters into gem clusters.
2) Some people don't like having to put in extra time turning boulders into blocks to get their construction materials in proper quantity. Presumably they aren't megaproject builders as such players are already used to having an army of masons for their construction works. So this is a complaint about "I need to get blocks made before I can build lots of workshops". As in, a complaint about extra micromanagement and time required to get non-megaproject infrastructure up (especially when a railway system needs to be set up). Well, the game is getting more fleshed out - Toady has a LOT of features in mind for future releases years down the line. You will always get 'more to do' as the game versions go up. In this particular case, you're getting a tradeoff with a much easier time cleaning up the 'trash boulders' from digging out your fortress.
3) I see a psychological aversion to the possibility of getting less than 25% because it's random. Players feeling this want an entirely deterministic mining mini-game, or at least feel 25% is too low for their comfort zone. Well... isn't the philosophy of Dwarf Fortress to go by the RNG, roguelike style? The community has adopted the "laugh as your dwarves meet their end in whatever messed up way" policy. It feels counter-intuitive that players can accept losing legendary[1] dwarves with rare 'perfect profiles'[2] to randomness[3], yet throw a tantrum at losing some rocks to randomness. Hmm, well I guess that's a dwarfy attitude in its own way.
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[1] highly sought after skill, e.g. weaponsmith
[2] ideal physical and mental stats, fitting personality traits, emotional attachment from history, physical description clicking well, etc
[3] victim of Fell Mood, burning sock fatal attraction, lucky thief's knife stab, etc