I have a Bobcat 442...not a large excavator by any stretch and it has a blade on the front for leveling/grading/pushing stuff around. Why don't you ever see large excavators with a blade? Probably a stupid question...
Kobelco makes a "Blade Runner" in a 160 size, which translates to about 36,000 pounds weight, biggest I've seen so far. I think basically the philosophy is that at a certain point it doesn't make economic sense to be pushing a little dirt with a big machine designed for digging. I think most customers would rather have the weight and expense of the blade directed toward more and faster digging, and with a large machine you can do more blading faster with a quick coupler and a cleanup bucket than you could with a dozer blade? Just guessing..... BTW, no such thing as a stupid question, we're all born knowing how to breathe, eat, and cry, the rest we all have to learn from somewhere, sometimes the hard way! LOL
I have seen pictures of modified 321 Cats with blades on them and personally I wouldn't want one as there is really no good reason to hang that much weight (it's already heavy enough to move) on the front and be in the way most of the time. When one gets into the larger class excavators (50K lb) a blade is not needed IMO. If you need that size excavator on a job that also requires blade or finish work you should have a dozer or track loader to take care of that.
Don't need one, we have large buckets. Many of my friends have modified loader buckets they just grab with their couplers. I carry a 10ft I beam on jobs when I need, it just grab it with the bucket and thumb. .
Blade on the smaller machines was probably added more as a stabilizer, than to function as a dozer blade. Larger machines have the weight, so stabilizers are not required. I do find the blade comes in handy, all 3 of my excavators have them.
volvo make the ecr305cl with option of a push blade mind you it adds around 4-5 ton to machine total weight its mainly an operators choice and dependent on terrain or working requirements it would be handy one job and in the way the next...
Blades on smaller machines make useful anchors to prevent the machine from moving because it's so light and the tracks simply slide across the ground. Other than that as posted above you don't need a blade when you have a bucket.