Actually ilvl increases coincide with the typical tome/raid cycling as new Raids are introduced, and even in 2.0 the ilevel of the gear you get from 2 dungeons increased by patch
Likewise the maximum ilevel would not change for two patches, the 2nd of which will try to help players get through the current hardcore raid fast, which is why the alliance raids dropped upgrade mats, why Thodian's Reign and Nidhogg's rage has weapons just shy off the maximum ilevel and also why the relic and dungeons get closer to the same cap in the 2nd patch of the cycle
- Initial Endgame Dungeons: i55
- 2.1: 60
- 2.2: 70
- 2.3: 80
- 2.4: 90
- 2.5: 100
The rising ilevels are more in part to a concept introduced within the middle of 2.X: Upgradable gear, previously exclusive to the relic but heavily simplified for tomestone gear. This concept alowed you to turn in a piece of certain gear along with a token to make it dyable and add 10 ilevels on it (before you ask, the upgraded gear is technically considered a new item so materia, and such are lost upon upgrading and you have to physically unequip it to upgrade it). With that removed, the Ironworks set would be on par with i100 dungeon sets (whether or not the Raid drops would be simialr depend on if the devs would treat tomestone gear an alternate endpoint or a mere steeping stone). That is not the only factor. The Gap had been widened by an increment of 10 because of the decision to have 2 difficulties for the raid, whch meant the Gordian gear (i90) drove a wedge between the two Tome sets, with the same thing happening again with Midas (and the decision to make crafted gear closer to the ilevel)
in 2.0 the pattern was Tome>Tome>Tome>Upgrade>Tome>Upgrade. In Heavenward the pattern is now Tome>Upgrade>Normal Alex>Tome>Upgrade>NM Alex/Craft>Tome>Upgrade, with each gear in these steps being in increments of 10