Why would line 1 on the w-2 (wages,tips,other compensation). Be a lot lower then box5 (Medicare wages and tips)

[Ashby]

It's usually because of your contribution to your retirement plan (401k, IRA, etc.). Also, it can be medical insurance premiums deducted from your income if you have a cafeteria plan. 

These items are pre-tax for income tax, but still subject to social security and medicare taxes.