One aspect of my role as an API support engineer is making sure that developer's questions are answered.
So, when a developer personally emails me a question, you would think that I would rush to answer it.
No. In fact, I usually ask them to post their question in the relevant group, and even if I know the answer to the question, I do not reveal it in my response.
This is because another aspect of my role is making sure that developer's questions are answered in a scalable manner.
If a developers emails me a question and I then answer it, that question and answer exist only inside our inboxes. They are absolutely undiscoverable by anyone else in the world, and basically useless to 99.9999999999999% of developers. However, if a developer posts a question in a forum and then receives an answer, that thread exists in the public group, it exists in the cached Google pages, it exists in the mail group archives - and most importantly, it exists in Google search results. That means that when another developer has the same question and search for it, they will find an answer - without even having to post their question. So, potentially 100% of developers can benefit from the question and answer. Now, *that* is scalable.
Now, a developer might think "But, I'm the only one with this question." This is nearly almost not the case, and it is not something that a developer can predict. Better safe than sorry, and share the question with the world.
Another aspect of my role is making sure that questions are answered in a timely manner.
If a developer emails me a question, and I happen to be quite busy then - with conferences, travel, launches, etc. - then I may not be able to respond for a few weeks. However, if a developer posts that question in the group, all of the group members may see it, and the chances are that atleast one of them know the answer and happen to have the time to respond. If they post in the group and don't get a response after a few days, it is fine protocol to ping the thread nicely, or hey, I don't even mind when a developer pings me personally and asks me to respond to the group thread.
So, oftentimes, when I ask a developer to post in a group, it's because I want them to get an answer faster than I can provide, and I happen to know that the Group is the best way to guarantee that.
Basically, the only times that I *happily* respond to a one-on-one email (or wave) is when the matter concerns personal account information and must be worked out on a case-by-case basis - for example, requests for higher geocoding limits, or the recent problems with some sandbox users not getting wave preview invites.
If you are a developer that I have sent to a group, please understand it is for your own good and the good of the world. Thanks for understanding!