Because there is no tax withholding on a code-G Form 1099-R, the details of the 1099-R forms that you entered into TurboTax are not included in your filed tax return. The only the result on Form 1040 lines 5a and 5b will be present.
TurboTax used to allow doing this with a single entry, but that presented problems for the case where the traditional 401(k) account had after-tax basis and the rollovers to the traditional IRA and to the Roth IRA were not the result of a single distribution request made to the 401(k) plan. In that case TurboTax had no way to determine how much of the after-tax basis to allocate to each of these rollovers without more input from the user. By requiring the user to split the form into two, it forces the user to properly allocate the after-tax basis. This problem is not present if there is no after-tax basis, but implementing two different ways to report a split distribution depending on the circumstances would likely be more confusing than helpful.
Things would get even more complicated if the code-G Form 1099-R included the reporting of an In-plan Roth Rollover. Although I don't recall anyone ever posting about such a situation, it's possible to have a single code-G Form 1099-R that reports the sum of an In-plan Roth Rollover, a rollover to a Roth IRA and a rollover to a traditional IRA, requiring the form to be split three ways.
