The fact you can't join a pool is discouraging to those who think they may never win a block . Being in a pool provides a sense of security that you will get rewarded for your efforts as opposed to your own personal luck. Whether this is true or not is irrelevant, it's just the perception of it being true.
In terms of probability you are wrong when you take the time factor out, unless it's too difficult for you to find a block within a time frame you're comfortable with then I guess a pool would be the only option, otherwise right now even a crappy dual core can find a block within a week.