As consumers we are told to shop price, and while I must agree that getting a fair price is important, it should not be the deciding factor in choosing one mortgage over another.  Trusting the most important financial activity you will do to the low cost provider is a recipe for disaster.

So what factors can play a role in the price of a mortgage.  "Why can't I get that price?"

Points - you way want to not pay points, or may chose to pay some.  The more points you pay the lower the rate you pay should be
No pre-pay penalty - most common in non-prime loans.  This can be expensive to get rid of
Escrow waiver - you want to pay your taxes and insurance bills when they come due
No fees or closing costs - Almost always an option, but the rate is higher to make up for the lack of upfront payment
80/15, or 80/20 - While you may save on no MI, you will pay a one time fee on the first to do this
Extended locks - rates are different for 15, 30, 45, 60 and so on.  The longer the lock, the higher the cost.
Loan product - An ARM, or I/O loan instead of a 30 year fixed
Loan term - the shorter the term the lower the rate
Loan amount - You may get charged more if the loan amount is below a certain amount and you might get a break if it is over another certain threshold
How you document your income - Pay stubs and bank statements always are the least expensive option.  The less you document the more expensive to loan will be.  It can get very expensive very quickly as well
Purpose - Non-purchase loans and loans to cash out equity often have surcharges
Occupancy  - Owner occupancy is the best, investment  the most expensive.
Property type - Multi family, and condos especially non-warrant able condo's can be more expensive.

Each of these things might be inexpensive on their own, for example waiving escrows might cost just a quarter point one time, but add a few of these up and you can quickly end up with a price that no longer sounds like the price you just saw on the Internet (not that it was real to start with). 

Asking for a rate before someone has asked you about questions like these is getting a rate that may or may not apply to you an your situation.  It's like going to the doctor and getting a prescription before getting a diagnoses.  It's malpractice.