Or people who play mods that modify mob drops, like Tale of Kingdoms which adds coin drops (which can only be picked up if you have an inventory slot available) and can add more than 500 items with, say, ten kills... especially if you have loot enchanted weapons.
My suggestion was to make an item block that basically gets local items floating in the world around it and absorbs them, similar to Pfaeff's "The Allocator" block. If the block itself didn't have physics-in the sense of 'walls' to stop you from walking into it-similar to water or lava, or air, then you could just pick up the items (that will fit into your inventory) as you pass through it.
Or... you'd just have to add an array (or arraylist, or linkedlist, or queue, or any of Java's collections) to keep a list of pointers to the items that it owns, to the superclass for all blocks, this way all block classes would inherent the ability automatically... Object oriented programming + Java FTW... I was in no way suggesting making them 'like chests' in the sense that you can right click them and 'view' said inventory. Just that it wouldn't despawn the drops.
The reason I'm suggesting this concept is because it preserves the conservation of energy/matter... a concept that very few games use. It annoys me that if I don't get to a drop quickly enough, or don't clear my inventory quickly enough, it fades into oblivion... (I won't go into the other breaks of conservation of matter) especially if I am nowhere near the drop, or not aware of the drop when it happens (like an item that requires a block, but is spawned where there isn't a block... i.e. Thaumcraft's crystals, but I've already mentioned this to that mod creator and see NO reason for you to have to give it attention).
Putting a collection within the superclass of all block classes (Block.class/.java I believe it's called) wouldn't add that much overhead to the game in terms of memory usage because it is simply storing a pointer to those items, and even removing them from the renderer's view which removes overhead (for the renderer anyway...). An idea that could even further help with reducing rendering overhead is to make any chunks that load outside of a given chunk radius load as height maps instead of chunks (i.e. a flat plain for the ground with things called 'Impostors' <assuming I remember correctly> to represent the objects above that 'ground'. 'Impostors' are basically two dimensional representations of models displayed on 'quads' (a flat 2D object in a 3D environment) that always face the player.) This would reduce the overhead of showing each and every block past that radius by simply showing a flat representation of them, which would even allow for things above ground, i.e. trees, mountains, etc. But I have no expectation of you doing that, it's something Mojang should do themselves, and frankly, I should mention there.
As for your question about why I play Minecraft in the first place... It certainly isn't to fill in gaps and holes in the map. It's to build and explore the world... When I want to build something on a flat surface and find a massive hole in the ground, and am not on creative, I don't want to risk my life building a single block layer bridge over it (which is stupid anyway as a single creeper would make the hole visible again), I would rather take the dirt I got from leveling the other side and just drop it to fill in the hole.
Minecraft is not necessarily created for mundane repetitive tasks, like moving a pile of sand from location a, to location b, with a pair of tweezers. And, really, I don't see why I should waste the resources for a shovel or bulldozer when I should simply be able to push the pile of sand with my hands and have the majority of it fall into place. (to use metaphoric imagery to show my point.
And, quite frankly, I've frequently quit playing Minecraft BECAUSE of the necessity to move a pile of sand with tweezers. I understand the lack of gravity for most blocks, but asking everyone to place block, jump, place block, jump, more than 500 times to fill in a hole is stupid, unrewarding, and boring. If I wanted that I'd quit college and get a grunt landscaping job... (this, of course, does NOT include things like building and decorating structures, but simply filling in holes. Building and decorating is/can be fun, filling in holes with anything other than sand/gravel is not.)