I am assuming that you are trying to replace the blades, not trying to remove the wiper arms. Klaus was telling you how to remove the arm.

I just replaced my blades on my 1998 V70 (base), and they did just pop off.

Have a look at the wiper image on the IPD site:
http://www.ipdusa.com/version.asp?strPageHistory=category&numSearchStartRecord=0&strParents=128,369,493&P_ID=1247&CAT_ID=493&V_ID=2429

The shiny rivet is one end of a small bar which is perpendicular to the blade. The bar fits into a slot in the end of the wiper arm. See IPD image:
http://www.ipdusa.com/version.asp?strPageHistory=category&numSearchStartRecord=0&strParents=128,369,493&P_ID=4467&CAT_ID=493&V_ID=11617

Hold the end of the wiper arm firmly and pull steadily on the blade frame. It is only held by friction and should pop out.
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Dave in Virginia; 1998 V70 T5(M): IPD MOTRONIC+ ECU Upgrade, Sport Muffler, IPD Strut Tower Brace; VDO Boost Gauge, IPD Anti-Sway Bars, Rocha ABS Control Unit, Koni FDS Struts and Shocks/// 1988 245 DL Wagon// 1967 MGB Roadster

No trick. The round end is a plastic cover that pops up, then use a 10mm to take off the nut.
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My name is Klaus and I am a V ♂ lv ♂ holic.