Defaulting to AND means that you aren't just searching for the most common term in your query that drowns out the rest. Also, adding terms narrows the query down rather than making it more general. This behavior strikes me as far more natural for "normal" people.
sure, i agree, except that they also apply this 'narrowing down' logic when insufficient or no results are returned, thinking the query needs to be more specific in order to work. i have observed the following sort of behaviour:
1. entering 'invisible marmalade teapot' and getting no results
2. changing to 'invisible marmalade teapot with tartan cosy', again nothing
3. so 'invisible marmalade teapot with tartan cosy in outer space', ditto
you get the idea...? it's just like in the real world, when you might go to a bookshop and say
You: do you have that new crime novel in stock?
Bookseller: er, i don't know which one you mean?
Y: the new crime novel by john grisham, pelican something or other?
B: oh, right, yes, here it is!
and everyone is happy.
default OR in a search engine would mean my first example eventually starting to return results about transparent space coffee pots with tartan cosies, ignoring the first few terms but the rest match, which is often helpful, particularly if you're doing an exploratory search for something where you aren't sure of the exact details.
Hm. I think perhaps a better way of putting it is that the hard AND issue is when people search using a natural language type query (I know about stop words, assume these are always filtered out) and include some extraneous term, so 'What is that new crime novel by John Grisham about a Penguin I think?' will return nothing, and no amount of extra terms added at the end will help, until you delete 'Penguin'... Of course it's anecdotal, but I still suspect it's one of the reasons for the hard AND to OR switch...
