Under Edit Options, Default Thread Subscription Mode, you can select your Default Thread Subscription Mode: Do Not Subscribe, and you will not be automatically subscribed to threads you create(post) or replies to threads which you respond.
Yes, I'm familiar with those pages. I just have like 35+ pages (700+ threads) of subscriptions and didn't see a "Delete All Subscriptions" (like all at once) option. Having to delete them one page at a time is time consuming. Once before I had like 100+ pages of subscriptions ........phew that took forever. I favor the subscriptions but if I don't clean out the old ones the file becomes HUGE.
Near the top of your subscriptions, right hand side, you can check a box which selects everything on the page. Then scroll down and the drop down box select delete. Not certain, but I think you can then select the next pages and do one delete for all selected.