Right - obviously not many of you understand what is involved on the day a couple go to the IVF clinic for egg collection/sample collection!
When you have IVF/ICSI your partner (the man) has to give a sperm Sample at the same time, or around the same time, that you (the woman) are having your eggs collected. To collect the eggs they sedate you and give you a pain killer and then they stick a needle into you via your vagina. Prior to this you have been on some pretty heavy fertility drugs in the days leading up to the egg collection.
Personally - having been through it myself - I much prefer the idea that my husband be able to produce his sample with the aid of a few magazines than having to stress about giving him a hand myself minutes before going through an egg collection!
As for sperm donors, I can't think that many of them would want to bring their partner (if they have one) into the clinic to help them with their sample.
Added to this - the sample has to make it from teh man's penis into a very small pot. Introducing another set of hands into this tricky situation is not really going to make it any easier to get a sample.