I paid for a lifetime subscription partly because it meant it was paid for, but also on the off-chance I lost my job before an annual subscription became due and I couldn't justify the cost of renewal (especially important now twins are on the way!).
That said, an annual subscription has the major benefit for customers that the provider has an huge incentive to keep you happy (and paying).
Had Sooloos been subscription based, I believe it would still be alive today. And, if I work out the maths, I think my MC200 would have cost me £2000 in depreciation over two years, if I had paid full retail.