It has become customary among bloggers to give credit to other bloggers if they were the source of a news item or blog idea, using the "hat tip", or HT. This is good form, because it acknowledges the work of others, and also forms a web between like minded bloggers.
Sometimes, so many bloggers are looking at the same information, there is no reason to HT or link to another blogger. The articles just happened to be posted in parallel.
I would like to see more people use the Hat Tip technique, if they don't have trackback cookies (Blogger.com doesn't).