It does give a good view into just how big a cut the Federal government is taking out of business. The illegals are basically working in the business environment we had in the early 20th century. None of the miscellaneous taxes and overhead deductions for both employer and employee, just cash on the barrel. Depending on how much you make, the government takes 50-100% on top of the paycheck you actually see. The illegals split the difference with their employers, and both come out ahead.
I've worked jobs where I knew how much it cost the business to pay me. At the last such job, 52% of the cost of my employment went to the government at various levels, with 48% of their cost being given to me in the form of a check. Any way you slice it, that isn't right for anyone and it encourages illegal employment.
If the government wants to reduce the incentive for illegal employment, all they have to do is eliminate the financial incentive for both employers and employees by greatly reducing the costs and overhead they impose on both parties via taxes and regulations when they do things by the book.
You are on the mark. Small businesses here (No. VA) without accounting/tax skills in house are much better off paying the illegal $10/hour unskilled wage than the $15/hour legal wage with the extra liability that it brings. The unskilled guy gets hurt, you can plausibly deny he ever worked for you. Same with taxes, if you screw up the unemployment tax or something like that, the state comes after you. If you pay an illegal under the table, nobody comes after you.