I am not sure what he means by saying that "there are only two verses for the Sudras". There are many more such verses which either contain instructions for a Sudra or are related to them in some way. Here are three of them for example:
2.24. Let twice-born men seek to dwell in those (above-mentioned countries); but a Sudra, distressed for subsistence, may reside
2.31. Let (the first part of) a Brahmana’s name (denote something) auspicious, a Kshatriya’s be connected with power, and a Vaisya’s with
wealth, but a Sudra’s (express something) contemptible
2.62. A Brahmana is purified by water that reaches his heart, a Kshatriya by water reaching his throat, a Vaisya by water taken into
his mouth, (and) a Sudra by water touched with the extremity (of his
So, which one among the three verses given above does he consider as not being written for the Sudras?
Similarly, we can show that number of verses which are about/on the Vaishyas is more than eight.
The three verses given above are talking about Vaishyas too so we just need to produce six more. I have given eight more:
2.65. (The ceremony called) Kesanta (clipping the hair) is ordained for a Brahmana in the sixteenth year (from conception); for a
Kshatriya, in the twenty-second; and for a Vaisya, two (years) later
2.80. The Brahmana, the Kshatriya, and the Vaisya who neglect (the recitation of) that Rik-verse and the timely (performance of the)
rites (prescribed for) them, will be blamed among virtuous men
2.127. Let him ask a Brahmana, on meeting him, after (his health, with the word) kusala, a Kshatriya (with the word) anamaya, a Vaisya (with
the word) kshema, and a Sudra (with the word) anarogya.
2.155. The seniority of Brahmanas is from (sacred) knowledge, that of Kshatriyas from valour, that of Vaisyas from wealth in grain (and
other goods), but that of Sudras alone from age
2.190. This duty is prescribed by the wise for a Brahmana only; but no such duty is ordained for a Kshatriya and a Vaisya.
3.13. It is declared that a Sudra woman alone (can be) the wife of a Sudra, she and one of his own caste (the wives) of a Vaisya, those two
and one of his own caste (the wives) of a Kshatriya, those three and
one of his own caste (the wives) of a Brahmana.
3.23. One may know that the first six according to the order (followed above) are lawful for a Brahmana, the four last for a Kshatriya, and
the same four, excepting the Rakshasa rite, for a Vaisya and a Sudra.
3.24. The sages state that the first four are approved (in the case) of a Brahmana, one, the Rakshasa (rite in the case) of a Kshatriya,
and the Asura (marriage in that) of a Vaisya and of a Sudra.
So, either we are not understanding what he is trying to say or he himself has got it all wrong.