@Brandon Hall, the CPA is not confused about rental real estate vs business real estate. He made no distinction. I actually used the example of the business sale in which one of the underlying assets is Sec 1250 real estate. The treatment of the real estate (even though owned by a business) is no different than rental real estate owned by an individual or an partnership. If you think so, please cite your support.
I've reviewed his research straight from the IRC and it all hangs together. Your citations of IRS publications seem to me to be not fully in context. Your research refers only to "depreciation recapture income" being treated in such-and-such a way, and the point is that Sec 1250 straight-line depreciation IS NOT "depreciation recapture income" at all, so any references to "depreciation recapture income" do not apply. It is in fact capital gains, albeit a special type of gain subject to a special rate. Thus your citations do not apply. Both the CPA's professional software, as well as Turbotax, agree.
You reference Section 453(i)(1), which is fine, but then 453(i)(2) has the definition for "recapture income", basically saying that it's only the portion of depreciation treated as ordinary income, and Section 1250 straight-line depreciation is NOT ordinary income, it's capital gains (technically called "unrecaptured section 1250 gain"). Please refer to the next section for support of what depreciation is treated as ordinary income (in short, straight line depreciation on Sec 1250 real estate is not ordinary income).
Quoting from IRS Pub 544:
Section 1250 Property
Gain on the disposition of section 1250 property is treated as ordinary income to the extent of additional depreciation allowed or allowable on the property. To determine the additional depreciation on section 1250 property, see Additional Depreciation, below.
Section 1250 property defined. This includes all real property that is subject to an allowance for depreciation and that is not and never has been section 1245 property. It includes a leasehold of land or section 1250 property subject to an allowance for depreciation.
Additional Depreciation
If you hold section 1250 property longer than 1 year, the additional depreciation is the actual depreciation adjustments that are more than the depreciation figured using the straight line method. For the treatment of unrecaptured section 1250 gain, see Capital Gains Tax Rate, later.