Here's my take on Donations...
What any one person chooses to do with his or her money is entirely up to them.
What any one person chooses to do with his or her signature/avatar is up to them as well. (So long as it stays within Forum Rules, but even then it's still up to them, they'll just get the ban hammer if they post something against the rules
)
I, currently as I'm posting this, have a Donation link in my signature, which I will probably remove now. The only reason it was put there was because people were asking for a link, I didn't have one, and I didn't know how to put the link in my avatar, (which I've figured out now) so I just created a quick link and threw it on there.
Now, the only reason I put it there was because people were asking for it. But in all seriousness, how can someone buy someone a beer or coffee around here if there isn't a link? So I had no issue putting it on there.
But, as to the issue on saying things like "Not necessary but welcome" or the like... I've said and can be quoted in multiple threads saying the same thing. The issue isn't the saying, it's the genuine feeling behind the saying. If you're sincere in that, then you truly do not care if anyone donates. You can write that all day, but if you don't truly feel that way, then you might as well just put up there "Give me money for doing this." I, personally, say what I mean... a man's word is only as good as he makes it to be. Everything I post is honest and truthful (to the best of my knowledge at least
) and I stick to my word.
Now, I, personally, have donated to those that have helped me on my path of development. I don't, however, expect anyone to donate to me though just because I might help them out with their development... Just being able to help someone is enough for me. But, if they want to donate, I'm not against it, and I'm not going to make it difficult to do so... They shouldn't get frustrated trying to do something nice, just trying to get a way to get the donation to me...
To me, I think more like sitting around a bar, I give someone some great advice on what they were having troubles with, they say "Hey, thanks a lot!" I'm turning to walk away and they stop me and Offer to buy me a drink. That's a donation.
Now, sitting at a restaurant, you get your food/drinks, you pay the bill, and what else? a Tip... While you're not paying for the food, and it's just a little more on top... That's NOT a donation. Tips are somewhat expected and how most waiter/waitresses make their money. Everyone knows that so there's even a general Percentage that is publicly "acceptable" to give. Or when the bagboy helps bring all your luggage to your room for you at a hotel... Also... not a donation. So when people start posting donation links in their threads or signature and make them big, or post things like, hey if I helped you, donate, or buy me a beer or whatever they have there, then they are the bagboy asking for money. There's the unspoken word there saying yeah, I helped you out, so you should pay me for it...
In my opinion, that's crossing the line. XDA is an open development community. If you're developing something for profits, I wish you the best of luck with it, but in my opinion, this isn't the place for that kind of thing...