This question makes no sense to me – I have not seen any hard data that showsto be significantly more vulnerable to comment spam than other blogging platforms' built-in comment systems.
WordPress itself, in fact, supports many comment systems via plugins, both local and hosted externally – including really featureful systems like, , and of course the new kid on the block, .
These systems have various strengths and weaknesses depending on the type of site/community being operated, and some of them (most prominently Facebook Comments) may seem more appealing in terms of effectiveness in blocking anonymous spam comments. But, for every pro, there's usually some other con waiting in the wings… In the case of FB comments, it's default loss of control of the comment data, and significant degradation of layout and formatting options.
If you want to host your comments locally, maintain total themeing control, etc – then WordPress' built-in comment system is still a good option – and combined with an anti-spam plugin like, or specific access/user verification steps, are certainly no more vulnerable to comment spam than other platforms' comparable built-in solutions.