Also, Abraham tithed 100s of years before the Law. If tithing was only under the Law then why did he tithe and why did God accept his tithes? Why didn't God say, "Oh Abraham, thou are a fool, it's more just about your heart, remember I put you under My grace - I don't want you giving Me the tithe..." Yet that is not what we find: we find that God received his tithes and poured out THE blessing on him in answer.
I have some pretty simple answers to those questions. PM me if you want to talk about it.
To summarize my position in general (since you didn't read through, understandably, there is a lot there) I don't think "we don't have to tithe anymore" exactly, I just think that the modern tradition/version/interpretation of tithing is difficult to support from a Biblical perspective.
I think if you've given 10% of your income to your local church, which has helped pay for your church's overhead costs, admin salaries, mortgage, new sound system/projector, Bible study materials, new library books, etc, you've been a good steward of the responsibilities you've taken on as a member of that church. But you have not yet given your tithe. And we do not want to rob God of His tithes...
I don't want to overstate the point here, so send me a PM if you want to discuss further.