Interestingly, in many topical online chats conversations like that are explicitly and actively discouraged. For example, if you have a math question in the Freenode ##math IRC channel and start with “hi” and/or “I have a math question”, you will likely get a stern “just ask” from a regular, or just stony silence. Since people still need an outlet for more idle chat, the rooms with no-nonsense chat policies tend to have a satellite off-topic channel where people engage in the longer form of smalltalk you describe.
Note that in this case, unlike a two-party in-person conversation, lots of people are listening but doing something else. If there is no activity for a while, and then there is some activity, that attracts their attention. If the activity is not interesting, or more precisely not the kind of thing for which they spend time in the channel, these people may consider their time/attention wasted. (The same argument applies to “why do you care about off-topic when nobody is talking anyway?”.)
I think that this is a perfectly good reason for it to be the conventional way to conduct a conversation in some cases and some media. Such rules also appeal to the “grow a thicker skin” culture, but that doesn’t mean they’re arbitrary.
It’s not so much the number of parties, as smalltalk is OK in general chat, it’s the off-topic noise that is discouraged, because of wasted time/attention, as you said, and possibly disrupted on-topic discussions.
Interestingly, in many topical online chats conversations like that are explicitly and actively discouraged. For example, if you have a math question in the Freenode ##math IRC channel and start with “hi” and/or “I have a math question”, you will likely get a stern “just ask” from a regular, or just stony silence. Since people still need an outlet for more idle chat, the rooms with no-nonsense chat policies tend to have a satellite off-topic channel where people engage in the longer form of smalltalk you describe.
Note that in this case, unlike a two-party in-person conversation, lots of people are listening but doing something else. If there is no activity for a while, and then there is some activity, that attracts their attention. If the activity is not interesting, or more precisely not the kind of thing for which they spend time in the channel, these people may consider their time/attention wasted. (The same argument applies to “why do you care about off-topic when nobody is talking anyway?”.)
I think that this is a perfectly good reason for it to be the conventional way to conduct a conversation in some cases and some media. Such rules also appeal to the “grow a thicker skin” culture, but that doesn’t mean they’re arbitrary.
It’s not so much the number of parties, as smalltalk is OK in general chat, it’s the off-topic noise that is discouraged, because of wasted time/attention, as you said, and possibly disrupted on-topic discussions.
I’ve known a lot of people to have http://www.nohello.com/ as their chat status message.
It makes sense that forum etiquette would be different.