Just word of mouth, but i think the fade in effect was to preserve a little virtual memory. Now I have no idea if this is even remotely true, nor can I be bothered researching into it. But yea.
Also, there are people in this world who like things that are there just for "eye-candy" and provide no real other use. Remember google is the most used search engine, so for people who arent really that tech savvy or whatever, they will go to google.com and type their queries in there instead of say using the search bar. And for them, this fade in effect might be interesting or cool. Not everyone is as uber-awesome techy like you cookie