It's the preference, Carl. As you said, when you were reading the ipad thread you were met with black squares. It's back to the dinner party. Would you be happier chatting with someone who you could see (visually picture) or someone with a black bag over their head. It's simply polite. If you look in the FAQ tab above, you'll see the only requirement for membership is to use your read name, not a company name or a nickname. So, no, it's not compulsory but it's just so much more pleasant for other members.
Sometimes there are glitches, as in poor Shirley who's been trying to upload, but others need encouragement.