Quote:
in 1954, when the Strat was introduced, amplifiers did not have a lot of high frequency response.


Nor did they (the amps) have a lot of power to reproduce and project the low frequencies. The amplitude of the low frequency vibration is affected to a greater degree than the highs in the immediate vicinity of the bridge. The low string simply cannot build its full energy oscillation (wave form) that close to the bridge. Slanting the pup was one way of getting a balanced tone under the then existing technological limitations by picking up the low signal at a point on the string where it (low freq oscillation) was better developed - away from the bridge and conversely, closer for the treble end of the spectrum.

Although the basic laws of physics haven't been altered in the interim, amp technology with frequency tailoring electronics has tremendously expanded the range of useable positions. One can pretty much have it their own way these days and usually have it work reasonably well.

Today they are slanted as much for tradition and marketing reasons as much as any technical reason. As always, YMMV. ;)