Pages 0, 1, 2, 3 are for configuration. They contain things like the UID and the Capability Container, some of which you cannot change, and some of which you should be very fucking careful changing.
I think Devilclarke left a bunch of empty pages at the beginning before writing the URI NDEF record because the forum URL is not very long, and he wanted to make sure that all the messed up bytes left over from whatever was previously written was completely overwritten. Wouldn’t want any vestigial data left over. Here’s an example of what a very similar NDEF record looks like on my tag using TagInfo, without the empty pages at the beginning:
[04] +r 03 26 D1 01 |␃&.␁|
[05] +r 22 55 00 68 |"U␀h|
[06] +r 74 74 70 73 |ttps|
[07] +r 3A 2F 2F 66 |://f|
[08] +r 6F 72 75 6D |orum|
[09] +r 2E 64 61 6E |.dan|
[0A] +r 67 65 72 6F |gero|
[0B] +r 75 73 74 68 |usth|
[0C] +r 69 6E 67 73 |ings|
[0D] +r 2E 63 6F 6D |.com|