Do senior physicists actually conduct research? Senior physicists constantly complain they spend too much time on administration, teaching, getting grants, serving in committees, peer-reviewing articles, supervising, etc. . Do senior physicists conduct research by getting their post-docs and graduate students to do all the intensive work for them?
 A: I can answer for experimental particle physics. The answer is yes.
Seniors are instrumental in motivating and, as you say, getting the money, overseeing that the experiment runs in group decisions, since experiments involve many groups. If they are any good  in physics they also have ideas on analysis, but the bulk of the work is carried by the graduate student whose thesis it is. Post docs have freedom of choice once the analysis stage is reached after having worked innumerable hours on hardware or software for the experiment . It is their chance of being original enough to succeed in someday being counted among the seniors.
A: Physics is top sport. When sports(wo)men age, they generaly discover that it becomes more and more difficult to compete. Some keep training and stay in the game till late age, but sooner or later they discover that the golden years are long past. No problem: these seniors carry a wealth of knowledge, and a position as coach, sports events organizer, etc. provides a natural second career.
Does a coach contribute to the results of his/her team? Sure (s)he does!
A: From the way the question is phrased, I take "senior physicist" to mean physicist who are advanced in administration rather than advanced in age.
The answer is that no, senior physicists do not contribute directly to research. At least, they do not contribute more than everyone else who works at a physics department. And do note that most of the people earn their money because of "physics" do not have an advanced physics degree and certainly are not "physicists". Instead, for each physicist there are large numbers of undergraduate students, graduate students, janitors, secretaries, various specialties such as plumbers, builders. Large experiments employ huge numbers of technicians, computer programmers, various blue-collar workers, accountants, lawyers, the list goes on and on. Finally, any physics group purchases equipment (example: personal computers, oscilloscopes, raw material) from companies that have little to do with physics. Since physics is an endeavor that is supported by taxes you might want to consider all taxpayers as contributing to physics. In this sense, sure, senior physicists do contribute.
The success of the human race is due to its unique organizational skill. Though most of the individuals do not understand this, the species is a classic herd animal. Almost all of the human race's domesticated animals are also herd animals, i.e. dogs, horses, chickens, pigs, ducks, cattle, donkeys, camel, llama, various fish, etc. The only common exception is the cat, hence the common expression, "like trying to herd cats".1
As a herd animal, humans do their activities in packs. They generally form hierarchical structures typically led by an older "alpha" male. This male spends his time keeping the other herd members in line and defending himself from aspirants to his position (which typically comes with improved access to females or various other perks). Their most impressive herd behavior are the large scale conflicts they organize. They use their most advanced available technology to hunt each other in packs. Humans make velociraptors look cuddly.
The success of the human species in physics is due to extreme specialization. Any given physicist knows almost nothing from direct observation. Instead, almost all knowledge is obtained from other physicists. This is the ultimate in specialization, there is no other known animal species anything like it. This specialization is extremely useful. For example, the number of physicists who actually measure the mass of the electron is only a tiny fraction of the total but all of them use the same number.
The stuff that goes on in a physics work groups is is all standard primate behavior that can be observed with more clarity in any jungle (the clarity arises because you will be examining a different species). Any sociologist can tell you these things. And there is at least one sociologist who specializes in physics, Harry Collins. To learn more about the sociology of physics, try picking up some of his fascinating books:
http://en.wikipedia.org/wiki/Harry_Collins
As a side note, the sociology of science is not a subject that is appreciated by very many physicists. They would instead prefer to believe that physics is an activity that is governed by a universal inclination to seek the truth. The only reason I ended up reading on the sociology of physics is because I was taught general relativity by Joseph Weber, and Weber was the primary subject of a book by Collins, "Gravity's Shadow: the search for gravitational waves". Naturally, when I saw the book on sale, I bought it, read it, and was fascinated by the description of physicists in it.
