In the world of entertainment, people... "borrow" ideas from each other all the time. I mean how many shows or movies have the same concept? I recall somewhere that there are only 7 original stories. So it's understandable that alot of stuff is similar.
Some things go too far. Any one remember Go-bots? At the time, many people thought that it was a rip-off of Transformers (actually, Go-bots came to the USA first).
It's the same for comics (since they are also part of the entertainment world). How many Batman (Night thrasher), Superman (Supreme), and Hulk (Pitt) clones are there out there? Even stories are used more than once. Really, how many nefarious plans can one guy have? There was an episode of South Park called "The Simpson's did it". In it, the mentioned that since Simpson's have been on the air for so long, there was no more new ideas out there. Many comic characters have been around for decades, so it is understandable that a story may repeat (or recycle) here and there.
Let's take a look at the Spider-Man/Obama comic. Image co-founder Eric Larsen was quoted as being upset that Marvel comics "stole" his idea from a Savage Dragon comic where his main character saves a president in an (almost) similar way. Ironically, he was also accused of doing the same thing with a Hulk comic (issue #420), where the main character (both Hulk, and Savage Dragon, in their own titles of course) had to face the dilemma of giving a friend a blood transfusion in the hopes that it would cure him of AIDS.
This one however takes the cake. According to Comic Mix, (another) Image co-founder, Rob Liefeld is going to have a massive multi-part inter-company crossover where his character "SMASH" declares war on his entire World. Just for the record, the pencils are supposedly unused pages from his Heroes Reborn work. I bet if World War Hulk wasn't successful, SMASH would not have been seen again....