Doesn't that just mean if you spam enough you get to spam even faster...?
I've got to say I wouldn't be in favour of removing the time limit between posting, it's minimal enough as it is and any time you can post a reply in under 20 seconds I've got serious doubts that it's really adding anything much to the topic - that's not to say you can't post a correct response quickly but whether it's particularly worthwhile is another issue. If you're lining up replies but not submitting to post them one after another then the question must be asked why are you doing that?
As for the 10 seconds between searches, it's a practical way to reduce/stop the impact of DDOS attacks as has been mentioned so that's not likely to change. However I'll be honest and admit that search isn't something I used often enough for that 10 second wait to bother me, now I might use it more often but there's no time restrictions as Zefan said.