ASRAAM, noone expects the Captain to be single pilot on a multi-crew aircraft. Delegation is part of the Captain's remit - when safe. Arguably there are times, like first flight, flight after maintenance (in this case BOTH of these), or even inexperienced FO when it could be prudent and responsible for the Captain to ensure that he does the walk round. Experience levels may even be similar but ultimately the Captain carries the can, not the FO. If the Captain does not have the combination of knowledge, experience and ability s/he should not be signing for the aircraft. Blaming engineers, engineering, management or FOs is passing the buck and not what the Captain is paid for.
However, you are right - the deicing process is one example where there are opportunities for aircraft to attempt to get airborne without the crew, let alone the Captain, being able to verify, if they wanted to, that what is supposed to have been done has in fact been done.
Another post mentions contractors - this is relevant to deicing. A contractor owes allegiance to a different company and will be under different pressures. The contractor does not fly on the aircraft .....
There are many opportunities for serious problems that are only fully recognised after serious incidents - my argument is that it is the Captain who can and should do his best to stop the holes lining up as s/he is the last link. Delegation may be the way to do this - but surely not when on the ground, with no emergencies unfolding, with no alarms going off...