So, Marissa ran an experiment where Google increased the number of search results to thirty. Traffic and revenue from Google searchers in the experimental group dropped by 20%. Ouch. Why? Why, when users had asked for this, did they seem to hate it? After a bit of looking, Marissa explained that they found an uncontrolled variable. The page with 10 results took .4 seconds to generate. The page with 30 results took .9 seconds. Half a second delay caused a 20% drop in traffic. Half a second delay killed user satisfaction.--Why Front End Performance Matters to Everyone, Not Just the High Traffic Giants via drunkenfist.com
This is a classic fallacy of correlation being mistaken for causation. How about 30 results overwhelming the user? Too much scrolling = forget it, I don't care anymore. Oh God, the Internet is so big. I'll never find what I'm looking for. That is what users think when you present them with 3 times the number of search results they're used to. That's the real explanation, not this response time explanation that is superficial at best. Response time is very important. Of course it is. But superior user experience design will trump negligible performance optimizations every day of the week.