Actually no, they didn't at first sorry. The first generation unibody released in 2008 did originally have a user replaceable battery. The second model however, released in 2009 removed the mechanisms needed to make it removable in favour of a larger battery.
For the 13" unibody models, I believe the batteries were easily replaced up until the late-2012 model. You just needed to remove the bottom cover and two tri-wing screws.
For previous models, the batteries were made to be easily removed without unscrewing anything.
Every MBP without retina screen has a removable battery (although you might need a tri-wing screwdriver like Audit13 pointed out). Replacing a battery by yourself could cost about $40-$50 - it is much cheaper than Apple's $120 which includes some labor fees and "Apple tax" in addition to a spare part cost. Actually even Retina models have a somewhat replaceable battery, but it requires a lot of manual efforts to properly remove this glued battery without breaking anything