Personal traditional and Roth IRA contributions are not reported on a W-2 form because they are not employer plans. Since some individuals have income from self-employment, alimony and other sources which qualify as compensation for making an IRA contribution, personal IRA contributions must be handled separately from Forms W-2.
A TSP *is* an employer plan, not an IRA, so it is handled by entering on TurboTax's W-2 form, just like a 401(k).
