I think form, in this case is misleading, and longer term over the season we're better off getting Giroud scoring than relying on Gervinho's hot streak continuing.
Otherwise, I think Goroud helps the team a little more even off form. So I'd have no issue taking the gamble.
If Wenger keeps picking Gervinho, he keeps scoring, and we keep winning, I'll be proven wrong, but my own feeling is that what Gervinho's done recently is more down to luck than form, and as such it's no reason to continue to select him.