There's a sense that these bonuses have escalated across editions, and that's generally true, but only in certain regards. It's not true in one aspect that may surprise people -- attack bonuses.
I've graphed the "automatic" attack bonuses that fighters gained in early editions of the game (OD&D in 1974, AD&D in 1979, and D&D Basic/Expert in 1981) along with 4th Edition (2008). These comparisons are necessarily rough because of the game's evolution, but they're still important.
Before showing the graphs and drawing conclusions, I'll lay out some of the ground rules.
The modifiers that are taken into account are the bonuses from the attacker's level, from Strength, from magic weapons, and from the expertise feat that is considered so essential in 4E. Fourth Edition has a regimented scale for magic weapons and Strength increases, unlike earlier editions that left these things in the hands of the DM and the random treasure tables. In early editions, Strength rarely changed after character creation. When it did, it was an exceptional occurrence. The amount of magic weaponry in the hands of early adventurers could vary wildly from campaign to campaign. Those scales are based on my experience as player, designer, and publisher.
The D&D B/X graph covers levels 1-15; OD&D and AD&D cover levels 1-20; and 4E covers levels 1-30. These are the levels included in the rulebooks. You can argue whether all of these levels really are playable, but the rulebooks claim that they are, and I'll take them at their word for this comparison.
With all of that out of the way, here are the graphs. Note that these are additive graphs; each line adds its values to the line below it, so that the top line on the graph shows the total value of all modifiers.
|Original D&D (1974)|
|Advanced D&D (1979)|
|D&D Basic/Expert (1981)|
|D&D 4th Edition (2008)|
|Four Editions Compared|
These are only the basics, of course. Fourth Edition injects the all-important class powers, which can boost the attack roll when it really matters. That's a somewhat different class of inflation, however, and I don't think it negates the importance of the progressions shown on these charts.
From my perspective, none of this is the real point. As interesting as this analysis is, it's not an end in itself. Instead, it lays the foundation for a much bigger question: Is there a better way to reward characters and players for gaining levels? That's a topic for later in the week.
P.S.: A quick note on why I chose these editions to compare. 4E is obvious. 2nd Ed. AD&D was omitted because it's basically identical to 1st Ed. Both OD&D and B/X were included because they employ different progressions from AD&D, and OD&D offers no bonus for high Strength. I find it interesting that in the end, those differences turn out to be more superficial than they appear. 3E doesn't appear for the simple reason that all my 3E manuals are packed away in boxes at the back of the storage room, and I didn't feel like digging them out.