Just to clarify some points made here:
This is not true. It's absolutely clear: there is no exemption for non-Argentine citizens. If you're resident here, you're subject to the tax. It's the law.
Two further points about this tax, which haven't been made here:
1. If you transfer 5% of the value of the value of your foreign-based assets to Argentina, the tax is halved.
2. The tax is denominated in pesos, and you pay in 5 instalments. With Argentine inflation what it is, the real rate is halved, assuming you keep your assets in hard currency.
By the same methods as the tax authorities in any country. In recent years, Argentina has signed up to OECD anti-tax evasion accords making it easy for them to get the bank account details of people in any OECD country. You could take a risk and not declare, leaving yourself open to tax evasion charges and large fines. On a more mundane level, you'd have to figure out a way to access your money outside the banking or cash transfer systems (every time you transfer money to Argentina, you have to sign a declaration on the origin of the funds).
So if aketada or anybody else really is determined to come and live in BA, it can be done; the ways of getting round all the problems are well discussed in this forum. It's just one of the complications of living in this country.
For my money, the best way would be still to legally base yourself in Uruguay. Then if you were really determined to live in BA, you could come over the river for months on end, bringing US$ 999,99 in cash with you every time ...