IPv6でのみListenしているように見えるが、実際はIPv4でもアクセス出来るのはなぜでしょうか？

netstatの結果だと、IPv6のport80はlistenしているが、IPv4のport80はlistenしていないように見えます。

# netstat -nat | grep -i listen
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:46391           0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:35868           0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:10050           0.0.0.0:*               LISTEN
tcp6       0      0 :::111                  :::*                    LISTEN
tcp6       0      0 :::80                   :::*                    LISTEN
tcp6       0      0 :::22                   :::*                    LISTEN
tcp6       0      0 :::25                   :::*                    LISTEN
tcp6       0      0 :::40415                :::*                    LISTEN
tcp6       0      0 :::10050                :::*                    LISTEN
tcp6       0      0 :::34343                :::*                    LISTEN

しかし、実際にIPv4のport80へアクセスすると、応答があります。

# curl 127.0.0.1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>403 Forbidden</title>
</head><body>
<h1>Forbidden</h1>
<p>You don't have permission to access /
on this server.</p>
</body></html>

tcpdumpしてみましたが、実際にIPv4にて応答しているようです。
（以下の結果はIPv6でアクセスした後、IPv4でアクセスした結果です。）

# tcpdump -i lo port 80
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
10:31:12.387377 IP6 localhost.53738 > localhost.http: Flags [S], seq 968427148, win 43690, options [mss 65476,sackOK,TS val 72593463 ecr 0,nop,wscale 7], length 0
00:22:33.663400 IP6 localhost.http > localhost.53738: Flags [S.], seq 1565811111, ack 968427149, win 43690, options [mss 65476,sackOK,TS val 72593463 ecr 72593463,nop,wscale 7], length 0
10:31:12.387407 IP6 localhost.53738 > localhost.http: Flags [.], ack 1, win 342, options [nop,nop,TS val 72593463 ecr 72593463], length 0
10:31:12.387473 IP6 localhost.53738 > localhost.http: Flags [P.], seq 1:74, ack 1, win 342, options [nop,nop,TS val 72593463 ecr 72593463], length 73: HTTP: GET / HTTP/1.1
10:31:12.387498 IP6 localhost.http > localhost.53738: Flags [.], ack 74, win 342, options [nop,nop,TS val 72593463 ecr 72593463], length 0
10:31:12.389620 IP6 localhost.http > localhost.53738: Flags [P.], seq 1:348, ack 74, win 342, options [nop,nop,TS val 72593465 ecr 72593463], length 347: HTTP: HTTP/1.1 403 Forbidden
10:31:12.389633 IP6 localhost.53738 > localhost.http: Flags [.], ack 348, win 350, options [nop,nop,TS val 72593466 ecr 72593465], length 0
10:31:12.390230 IP6 localhost.53738 > localhost.http: Flags [F.], seq 74, ack 348, win 350, options [nop,nop,TS val 72593466 ecr 72593465], length 0
10:31:12.391606 IP6 localhost.http > localhost.53738: Flags [F.], seq 348, ack 75, win 342, options [nop,nop,TS val 72593467 ecr 72593466], length 0
10:31:12.391643 IP6 localhost.53738 > localhost.http: Flags [.], ack 349, win 350, options [nop,nop,TS val 72593468 ecr 72593467], length 0
10:31:30.095105 IP localhost.34130 > localhost.http: Flags [S], seq 691767966, win 43690, options [mss 65495,sackOK,TS val 72611171 ecr 0,nop,wscale 7], length 0
21:30:08.961986 IP localhost.http > localhost.34130: Flags [S.], seq 4181075012, ack 691767967, win 43690, options [mss 65495,sackOK,TS val 72611171 ecr 72611171,nop,wscale 7], length 0
10:31:30.095157 IP localhost.34130 > localhost.http: Flags [.], ack 1, win 342, options [nop,nop,TS val 72611171 ecr 72611171], length 0
10:31:30.095797 IP localhost.34130 > localhost.http: Flags [P.], seq 1:74, ack 1, win 342, options [nop,nop,TS val 72611172 ecr 72611171], length 73: HTTP: GET / HTTP/1.1
10:31:30.095853 IP localhost.http > localhost.34130: Flags [.], ack 74, win 342, options [nop,nop,TS val 72611172 ecr 72611172], length 0
10:31:30.097912 IP localhost.http > localhost.34130: Flags [P.], seq 1:348, ack 74, win 342, options [nop,nop,TS val 72611174 ecr 72611172], length 347: HTTP: HTTP/1.1 403 Forbidden
10:31:30.097922 IP localhost.34130 > localhost.http: Flags [.], ack 348, win 350, options [nop,nop,TS val 72611174 ecr 72611174], length 0
10:31:30.099390 IP localhost.34130 > localhost.http: Flags [F.], seq 74, ack 348, win 350, options [nop,nop,TS val 72611175 ecr 72611174], length 0
10:31:30.099537 IP localhost.http > localhost.34130: Flags [F.], seq 348, ack 75, win 342, options [nop,nop,TS val 72611175 ecr 72611175], length 0
10:31:30.099561 IP localhost.34130 > localhost.http: Flags [.], ack 349, win 350, options [nop,nop,TS val 72611175 ecr 72611175], length 0

なぜIPv4にてport80へアクセスしても応答があるのでしょうか。
netstatで表示されていなくとも、応答可能な場合はあるのでしょうか。

よろしくお願いいたします。