The difference is you made a false assumption that 1 month = 4 weeks. This is only true for ONE month (most of the time, hi leap years!) February. Every single other month has 2-3 more days which makes up the difference.

• Jan: 4 w + 3 d
• Feb: 4 w + 0 d (1 d in leap years)
• Mar: 4 w + 3 d
• Apr: 4 w + 2 d
• May: 4 w + 3 d
• Jun: 4 w + 2 d
• Jul: 4 w + 3 d
• Aug: 4 w + 3 d
• Sep: 4 w + 2 d
• Oct: 4 w + 3 d
• Nov: 4 w + 2 d
• Dec: 4 w + 3 d

Totals: 48 w + 29 or 30 d = 52 w + 1 or 2 d