Can you deduct the $10,000 as a business expense?
Maybe not - story here.
The IRS is saying since a domain is an intangible asset it requires amortization of the cost over 15 years.
What's the impact?
If you're in the 25% tax bracket a $10,000 deduction immediately saves you $2500 in taxes. If you amortize over 15 years that is a $667 yearly deduction and only $167 per year in tax savings.
There is a de minimis rule so this issue should not apply to domain purchases of $5000 or less.
Bottom line: don't be casually making big domain purchases without considering the tax implications in your business plan.